Infectious Disease — GI

114. Diverticulitis

uncomplicated (IV antibiotics) · complicated (abscess/perforation/obstruction/fistula) · cover gram-neg + anaerobes with cefepime + metronidazole (this formulary) · drain larger abscesses · Super Compact

Sx: LEFT lower quadrant pain (sigmoid most common), fever, change in bowel habits (constipation/diarrhea), nausea, anorexia; localized tenderness ± palpable mass · complicated: peritonitis (diffuse pain/guarding/rebound), high fever, obstruction (distension/vomiting), pneumaturia/fecaluria (fistula) · (LLQ pain + fever in an adult is diverticulitis until imaged; the CT does two jobs — confirms the diagnosis and tells you if it's complicated, which changes everything)

Neg: denies missed complicated disease (abscess, perforation, obstruction, fistula — needs drainage/surgery) · denies missed free perforation/peritonitis (emergent surgery) · denies missed malignancy mimicking (colonoscopy after recovery) · denies inadequate anaerobic coverage (cefepime needs metronidazole) · denies missed alternative LLQ cause

SHx: prior diverticulitis episodes (recurrence), known diverticulosis, immunocompromise (steroids/transplant — higher complication/perforation risk + atypical presentation), constipation/low-fiber diet, NSAID use, prior abdominal surgery, malignancy history

Etiology: micro-perforation/inflammation of a colonic diverticulum → peridiverticular infection · colonic flora (polymicrobial): gram-negatives (E. coli, Klebsiella) + anaerobes (Bacteroides — the metronidazole target) · complications: abscess (walled-off), free perforation (peritonitis), obstruction (stricture), fistula (colovesical most common)

RF: diverticulosis · prior episodes · low-fiber diet/constipation · obesity · NSAIDs · smoking · immunocompromise (severe/perforated disease) · age

Data: CT abdomen/pelvis with contrast (the key study — confirms diagnosis, grades complicated vs uncomplicated, finds abscess/perforation/free air/obstruction/fistula) · CBC (leukocytosis), CMP, lactate, blood cultures if systemic/septic, lipase, UA (fistula); pregnancy test · colonoscopy 6–8 weeks AFTER recovery (exclude malignancy — not acutely)

DDx: diverticulitis · colorectal malignancy (can mimic — scope after) · IBD (Crohn's/colitis) · ischemic colitis · appendicitis (if redundant sigmoid/right-sided) · gynecologic (ovarian, PID, ectopic) · infectious colitis · nephrolithiasis · abscess

Home Meds: NPO/bowel rest if significant; hold NSAIDs (associated with perforation); reconcile + renally dose abx; hold anticoagulants if procedure/surgery likely; resume diet/meds as tolerated with recovery

Plan

CONSULT: Surgery (complicated disease — perforation/peritonitis/obstruction/fistula, or failure of medical therapy; recurrent disease surgical planning) · Interventional Radiology (percutaneous drainage of abscess ≥~3–4 cm) · GI (post-recovery colonoscopy) · ICU (perforation/sepsis)

– SOURCE CONTROL for complicated disease: percutaneous (IR) drainage of larger abscesses (≥~3–4 cm); emergent surgery for free perforation/diffuse peritonitis/obstruction (Hartmann's or resection ± diversion); smaller abscesses (<~3–4 cm) often resolve with antibiotics alone
– EMPIRIC ANTIBIOTICS (gram-negatives + anaerobes; THIS FORMULARY uses cefepime, NOT piperacillin-tazobactam — add metronidazole):
  • Inpatient/IV (uncomplicated requiring admission, OR complicated): cefepime 2 g IV q8h + metronidazole 500 mg IV q8h (cefepime for gram-negatives incl Pseudomonas if healthcare-associated/severe; metronidazole for anaerobes — together replace Zosyn); a reasonable alternative for community-acquired without Pseudomonas risk is ceftriaxone 1–2 g IV q24h + metronidazole 500 mg IV q8h
  • Single-agent alternative (if formulary): ertapenem 1 g IV q24h (covers anaerobes alone, community-acquired)
  • Add vancomycin/antifungal only if healthcare-associated/severe/immunocompromised concerns per cultures/ID
– NARROW + STEP DOWN: IV→PO once afebrile, abdominal pain/tenderness improving, WBC trending down, tolerating diet, and (if complicated) source controlled/abscess drained or resolving
  • Oral step-down (retain gram-negative + anaerobic cover): amoxicillin-clavulanate 875 mg PO q12h, OR (ciprofloxacin 500 mg PO q12h or levofloxacin 750 mg PO daily) + metronidazole 500 mg PO q8h
  • DURATION: uncomplicated ~4–7 days total (short courses validated for uncomplicated disease; some selected mild outpatient cases need no antibiotics, but admitted/IV cases are treated); complicated/abscess: longer (~7–14 days, individualized by source control + response)
– Supportive: bowel rest → advance diet as tolerated, IV fluids, analgesia (avoid NSAIDs), antiemetics, VTE prophylaxis
– The CT is the pivot: it confirms diverticulitis and, more importantly, sorts uncomplicated from complicated — because a phlegmon resolves on antibiotics while an abscess over a few centimeters needs a drain and a free perforation needs a surgeon. The antibiotic principle is the recurring one in this handbook: cover gut gram-negatives and anaerobes, and since the pharmacy carries cefepime rather than Zosyn, that means cefepime plus metronidazole. Courses are short for uncomplicated disease — four to seven days — and don't forget the interval colonoscopy a few weeks out to make sure you weren't treating a perforated cancer.
– PT/OT: mobilization; post-op recovery if surgical
– Trend: abdominal exam, fever curve, WBC, lactate, diet tolerance, drain output if drained, repeat imaging if not improving (undrained/enlarging abscess)
– Escalation triggers: peritonitis/free perforation/obstruction → emergent surgery; failure to improve on antibiotics → re-image (undrained abscess) + drain/surgery; abscess ≥3–4 cm → IR drainage; sepsis → broaden + ICU
– Discharge checklist: improving + afebrile + tolerating diet + (if complicated) source controlled; oral regimen + total duration/stop date specified; interval colonoscopy 6–8 weeks scheduled (malignancy exclusion) if not recently done; high-fiber diet counseling + recurrence prevention; surgery follow-up (recurrent/complicated — elective resection discussion); return precautions (worsening/spreading pain, high fever, vomiting/obstruction, inability to eat, peritoneal signs)

114. Diverticulitis

complete reference · uncomplicated (IV antibiotics) + complicated (abscess) · CT-driven, cefepime + metronidazole, drain larger abscesses, interval colonoscopy · Full Card

Symptoms / Associated Sx

• Left lower quadrant pain (the sigmoid is most common), fever, a change in bowel habits (constipation or diarrhea), nausea, and anorexia; localized tenderness, sometimes with a palpable mass

• Complicated disease: peritonitis (diffuse pain, guarding, rebound), high fever, obstruction (distension, vomiting), and pneumaturia or fecaluria (a fistula)

• LLQ pain with fever in an adult is diverticulitis until imaged; the CT both confirms the diagnosis and identifies complicated disease, which changes everything

Neg

• Pt denies a missed complicated disease (abscess, perforation, obstruction, fistula — needing drainage or surgery)

• Pt denies a missed free perforation or peritonitis (emergent surgery) and a missed malignancy mimicking diverticulitis (a colonoscopy after recovery)

• Pt denies inadequate anaerobic coverage (cefepime needs metronidazole) and a missed alternative LLQ cause

Social History (SHx)

• Prior diverticulitis episodes (recurrence) and known diverticulosis

• Immunocompromise (steroids, transplant — with higher complication and perforation risk and an atypical presentation), constipation or a low-fiber diet, and NSAID use

• Prior abdominal surgery and malignancy history

Main Etiology

• Micro-perforation and inflammation of a colonic diverticulum cause a peridiverticular infection

• Colonic flora are polymicrobial: gram-negatives (E. coli, Klebsiella) plus anaerobes (Bacteroides — the metronidazole target)

• Complications: an abscess (walled-off), free perforation (peritonitis), obstruction (stricture), and fistula (colovesical most common)

RF

• Modifiable: a low-fiber diet or constipation, obesity, NSAIDs, and smoking

• Non-modifiable: diverticulosis, prior episodes, immunocompromise (severe or perforated disease), and age

Data

• CT of the abdomen/pelvis with contrast (the key study — confirming the diagnosis, grading complicated versus uncomplicated, and finding an abscess, perforation, free air, obstruction, or fistula)

• CBC (leukocytosis), CMP, lactate, blood cultures if systemic or septic, lipase, and urinalysis (fistula); a pregnancy test

• Colonoscopy 6–8 weeks after recovery (to exclude malignancy — not acutely)

DDx

Diverticulitis · colorectal malignancy (can mimic — scope afterward) · IBD (Crohn's, colitis) · ischemic colitis · appendicitis (with a redundant sigmoid or right-sided disease) · a gynecologic cause (ovarian, PID, ectopic) · infectious colitis · nephrolithiasis · an abscess

Home Meds

• NPO or bowel rest if significant; hold NSAIDs (associated with perforation)

• Reconcile and renally dose antibiotics; hold anticoagulants if a procedure or surgery is likely

• Resume diet and medications as tolerated with recovery

Plan

CONSULT: Surgery (complicated disease — perforation, peritonitis, obstruction, fistula, or failure of medical therapy; recurrent-disease surgical planning) · Interventional Radiology (percutaneous drainage of an abscess ≥~3–4 cm) · GI (post-recovery colonoscopy) · ICU (perforation, sepsis)

• Source control for complicated disease: percutaneous (IR) drainage of larger abscesses (≥~3–4 cm); emergent surgery for free perforation, diffuse peritonitis, or obstruction (a Hartmann's procedure or resection with diversion); smaller abscesses (<~3–4 cm) often resolve with antibiotics alone

• Empiric antibiotics (gram-negatives and anaerobes; this formulary uses cefepime, not piperacillin-tazobactam — add metronidazole):

• • Inpatient/IV (uncomplicated requiring admission, or complicated): cefepime 2 g IV every 8 hours plus metronidazole 500 mg IV every 8 hours (cefepime for gram-negatives including Pseudomonas if healthcare-associated or severe, metronidazole for anaerobes — together replacing Zosyn); a reasonable alternative for community-acquired disease without Pseudomonas risk is ceftriaxone 1–2 g IV every 24 hours plus metronidazole 500 mg IV every 8 hours

• • Single-agent alternative (if on formulary): ertapenem 1 g IV every 24 hours (covering anaerobes alone, for community-acquired disease)

• • Add vancomycin or an antifungal only for healthcare-associated, severe, or immunocompromised concerns per cultures and ID

• Narrow and step down: switch IV to PO once the patient is afebrile, the abdominal pain and tenderness are improving, the white count is trending down, a diet is tolerated, and (if complicated) the source is controlled with the abscess drained or resolving

• • Oral step-down (retaining gram-negative and anaerobic coverage): amoxicillin-clavulanate 875 mg PO every 12 hours, or (ciprofloxacin 500 mg PO every 12 hours or levofloxacin 750 mg PO daily) plus metronidazole 500 mg PO every 8 hours

• • Duration: uncomplicated about 4–7 days total (short courses are validated for uncomplicated disease; some selected mild outpatient cases need no antibiotics, but admitted IV cases are treated); complicated disease or an abscess longer (about 7–14 days, individualized by source control and response)

• Supportive care: bowel rest advancing to diet as tolerated, IV fluids, analgesia (avoiding NSAIDs), antiemetics, and VTE prophylaxis

• PT/OT: mobilization, with post-operative recovery if surgical

• Trend: the abdominal exam, the fever curve, WBC, lactate, diet tolerance, drain output if drained, and repeat imaging if not improving (an undrained or enlarging abscess)

• Escalation triggers: peritonitis, free perforation, or obstruction → emergent surgery; failure to improve on antibiotics → re-image (an undrained abscess) and drain or operate; an abscess ≥3–4 cm → IR drainage; sepsis → broaden and ICU

• Discharge checklist: improving, afebrile, and tolerating a diet, with (if complicated) the source controlled; an oral regimen with a total duration and stop date specified; an interval colonoscopy at 6–8 weeks scheduled (malignancy exclusion) if not recently done; high-fiber diet counseling and recurrence prevention; surgery follow-up (recurrent or complicated disease — an elective resection discussion); return precautions for worsening or spreading pain, high fever, vomiting or obstruction, inability to eat, or peritoneal signs

Red Flags

• Free perforation, diffuse peritonitis, or obstruction → emergent surgery

• An abscess ≥3–4 cm → percutaneous drainage; antibiotics alone often won't clear it

• Failure to improve on antibiotics → re-image for an undrained or enlarging abscess

• Immunocompromise → higher perforation risk with a blunted presentation; have a lower threshold for complicated disease

• A first episode in an older adult → arrange interval colonoscopy to exclude a perforated malignancy

Senior IM Resident Pearls

• The CT is the pivot. It confirms diverticulitis and, more importantly, sorts uncomplicated from complicated — which decides whether the patient needs antibiotics, a drain, or a surgeon.

• Cefepime plus metronidazole covers the colon. Gut gram-negatives and anaerobes both need treatment, and since the pharmacy carries cefepime rather than Zosyn, the metronidazole partner is mandatory.

• Drain the bigger abscess. A collection over a few centimeters needs percutaneous drainage; a smaller phlegmon usually resolves on antibiotics alone.

• Courses are short for uncomplicated disease. Four to seven days is enough — resist the old reflex to treat for two weeks.

• Don't skip the interval colonoscopy. A few weeks after recovery, scope to make sure you weren't treating a perforated cancer.

• Avoid NSAIDs. They're associated with perforation, so manage pain with other agents during the acute episode.

• Common mistake: calling everything "uncomplicated" without reading the CT carefully — a small abscess or a sealed perforation changes the drainage plan and the duration.

Infectious Disease — Endovascular

115. Infective Endocarditis

native & prosthetic valve · IV drug use · persistent bacteremia · 3 blood culture sets + echo + Duke criteria · prolonged IV therapy · surgery for the right indications · Super Compact

Sx: fever (most common), new/changed murmur, fatigue, night sweats, weight loss; embolic/immune phenomena: septic emboli (stroke, splenic/renal infarcts, septic pulmonary emboli in right-sided/IVDU), Janeway lesions, Osler nodes, Roth spots, splinter hemorrhages, glomerulonephritis · heart failure (valve destruction) · (persistent S. aureus bacteremia, a new murmur, or an embolic stroke with fever should make you think endocarditis and get an echo — IE is a clinical-plus-echo-plus-culture diagnosis, not one test)

Neg: denies missing IE in S. aureus/persistent bacteremia (always echo) · denies missing surgical indications (heart failure, uncontrolled infection, large/mobile vegetation with emboli, abscess, prosthetic dehiscence — surgery saves lives) · denies missing complications (heart block from root abscess, mycotic aneurysm, metastatic foci, CNS emboli) · denies stopping therapy early

SHx: IV drug use (right-sided/tricuspid, S. aureus), prosthetic valve/valve repair (prosthetic IE), prior IE, congenital/structural heart disease, recent dental/surgical/invasive procedure, indwelling lines/hemodialysis, immunocompromise, poor dentition

Etiology: S. aureus (most common overall, esp acute + IVDU), viridans streptococci (subacute, dental), enterococci (GU/GI source, elderly), coag-neg staph (prosthetic valve, esp early), HACEK, Candida (IVDU/prosthetic/lines) · prosthetic: early (≤1 yr — coag-neg staph, S. aureus) vs late (community organisms) · culture-negative (prior abx, fastidious — Coxiella/Bartonella)

RF: IVDU · prosthetic valve/structural heart disease · prior IE · indwelling lines/hemodialysis · immunocompromise · poor dentition/recent procedure

Data: THREE sets blood cultures from separate sites, spaced, BEFORE antibiotics (persistent bacteremia is a major Duke criterion) · echocardiography: TTE first, then TEE (more sensitive — vegetations, abscess, prosthetic, leaflet destruction) · Modified Duke criteria · CBC, CMP, ESR/CRP, UA (hematuria/GN), ECG (new heart block → root abscess); imaging for emboli (CT head/abd, etc.); dental eval

DDx: infective endocarditis · bacteremia without IE · non-infective (marantic/Libman-Sacks) endocarditis · vasculitis · atrial myxoma · other causes of FUO/embolic stroke · line infection without IE · rheumatologic disease

Home Meds: anticoagulation is nuanced (don't routinely start; risk of hemorrhagic transformation of septic emboli — coordinate with cardiology/neuro; continue for strict mechanical-valve indications with care) · reconcile + renally dose abx · plan long-term IV access (PICC) for prolonged course · addiction treatment (IVDU)

Plan

CONSULT: Infectious Disease (regimen + duration — essential) · Cardiology (echo, heart failure, monitoring) · Cardiothoracic Surgery (EARLY — surgical indications: HF, uncontrolled infection, emboli/large vegetation, abscess, prosthetic dehiscence) · Neurology (CNS emboli) · Addiction Medicine (IVDU) · Dental

– DIAGNOSE rigorously: 3 sets blood cultures before antibiotics + TTE→TEE + apply Modified Duke criteria; identify the organism (durations + regimen depend on it)
– EMPIRIC ANTIBIOTICS (only after cultures drawn; for acutely ill/unstable — then narrow):
  • Native valve, acute / IVDU: vancomycin IV (covers MRSA + most gram-positives) ± gram-negative coverage per risk
  • Prosthetic valve: vancomycin + gentamicin + rifampin (per ID — biofilm/staph) pending cultures
  (if a stable subacute presentation, it's often best to await cultures before starting — coordinate with ID)
– TARGETED therapy (organism + valve type — ID-directed; representative):
  • MSSA native → cefazolin 2 g IV q8h (or nafcillin) × ~6 weeks; MRSA → vancomycin × ~6 weeks
  • Viridans strep (susceptible) → ceftriaxone or penicillin × ~4 weeks (native)
  • Enterococcus → ampicillin + ceftriaxone (or + gentamicin) × ~4–6 weeks
  • Prosthetic valve staph → add rifampin + gentamicin to the primary agent × ≥6 weeks
– DURATION: prolonged IV — typically ~4–6 weeks (from first negative culture for staph), longer (≥6 wk) for prosthetic valves; right-sided IVDU MSSA may be shorter (~2 weeks) in selected uncomplicated cases per ID
– STEP-DOWN note: traditionally completed IV; selected stabilized left-sided IE may transition to an oral regimen after initial IV control per ID (POET trial — partial oral therapy non-inferior in stabilized, selected patients) — ID/cardiology-directed, not routine; otherwise OPAT/PICC to complete IV
– SURGERY (cardiothoracic — involve early for): heart failure from valve dysfunction, uncontrolled/persistent infection despite appropriate abx, perivalvular abscess/heart block, large mobile vegetations with recurrent emboli, prosthetic valve dehiscence/severe dysfunction, fungal/highly resistant IE
– REPEAT blood cultures q24–48h to document clearance; treat heart failure; manage emboli; addiction treatment + harm reduction (IVDU)
– Endocarditis is a three-legged diagnosis — cultures, echo, and Duke criteria — so draw three sets of blood cultures before antibiotics and get a TEE; never let a single negative test close the question in the right patient. Treatment is a marathon (four to six weeks IV, longer for prosthetic valves), and the recently validated POET data means selected, stabilized left-sided cases can finish orally under ID guidance — but that's a deliberate decision, not a default. The single most important non-antibiotic move is calling cardiac surgery early: heart failure, an abscess with new heart block, a big mobile vegetation throwing emboli, or uncontrolled infection are all reasons valve surgery saves the patient.
– PT/OT: per status; neuro rehab if embolic stroke
– Trend: repeat blood cultures (clearance), fever curve, daily cardiac exam (new murmur/HF), ECG (new block → abscess), echo as indicated, embolic surveillance, end-organ function
– Escalation triggers: new heart failure → urgent surgery; persistent bacteremia despite therapy → TEE for abscess/uncontrolled infection + surgery; new heart block → root abscess → surgery; embolic events/large vegetation → surgical discussion; septic shock → ICU
– Discharge checklist: blood cultures cleared + clinically stable + surgical questions addressed; full prolonged regimen via OPAT/PICC (or validated oral step-down) with total duration/stop date specified; ID + cardiology follow-up + repeat echo plan; dental care; addiction treatment linkage (IVDU); anticoagulation plan clarified; return precautions (recurrent fever, new neuro deficits, dyspnea/edema — HF, embolic symptoms, line issues)

115. Infective Endocarditis

complete reference · IVDU + prosthetic valve + persistent bacteremia · 3 cultures + TEE + Duke, prolonged therapy, early surgery for indications · Full Card

Symptoms / Associated Sx

• Fever (the most common finding), a new or changed murmur, fatigue, night sweats, and weight loss

• Embolic and immune phenomena: septic emboli (stroke, splenic or renal infarcts, septic pulmonary emboli in right-sided or IVDU disease), Janeway lesions, Osler nodes, Roth spots, splinter hemorrhages, and glomerulonephritis

• Heart failure from valve destruction

• Persistent S. aureus bacteremia, a new murmur, or an embolic stroke with fever should prompt thought of endocarditis and an echo — IE is a clinical-plus-echo-plus-culture diagnosis, not a single test

Neg

• Pt denies missing IE in S. aureus or persistent bacteremia (always echo)

• Pt denies missing surgical indications (heart failure, uncontrolled infection, a large or mobile vegetation with emboli, an abscess, prosthetic dehiscence — surgery saves lives)

• Pt denies missing complications (heart block from a root abscess, a mycotic aneurysm, metastatic foci, CNS emboli) and denies stopping therapy early

Social History (SHx)

• IV drug use (right-sided or tricuspid disease, S. aureus), a prosthetic valve or valve repair (prosthetic IE), and prior IE

• Congenital or structural heart disease, and a recent dental, surgical, or invasive procedure

• Indwelling lines or hemodialysis, immunocompromise, and poor dentition

Main Etiology

• S. aureus (the most common overall, especially in acute disease and IVDU), viridans streptococci (subacute, dental), enterococci (a GU or GI source, the elderly), coagulase-negative staph (prosthetic valves, especially early), HACEK organisms, and Candida (IVDU, prosthetic valves, lines)

• Prosthetic disease: early (≤1 year — coagulase-negative staph, S. aureus) versus late (community organisms)

• Culture-negative disease (prior antibiotics, fastidious organisms — Coxiella, Bartonella)

RF

• Modifiable: IV drug use, indwelling lines or hemodialysis, and poor dentition or recent procedures

• Non-modifiable: a prosthetic valve or structural heart disease, prior IE, and immunocompromise

Data

• Three sets of blood cultures from separate sites, spaced, before antibiotics (persistent bacteremia is a major Duke criterion)

• Echocardiography: TTE first, then TEE (more sensitive — vegetations, abscess, prosthetic involvement, leaflet destruction)

• The Modified Duke criteria

• CBC, CMP, ESR/CRP, urinalysis (hematuria, glomerulonephritis), and an ECG (new heart block → a root abscess); imaging for emboli (CT head, abdomen); and a dental evaluation

DDx

Infective endocarditis · bacteremia without IE · non-infective (marantic or Libman-Sacks) endocarditis · vasculitis · an atrial myxoma · other causes of fever of unknown origin or embolic stroke · a line infection without IE · rheumatologic disease

Home Meds

• Anticoagulation is nuanced — don't routinely start it (risk of hemorrhagic transformation of septic emboli; coordinate with cardiology and neurology); continue it for strict mechanical-valve indications with care

• Reconcile and renally dose antibiotics; plan long-term IV access (a PICC) for the prolonged course

• Arrange addiction treatment for IVDU

Plan

CONSULT: Infectious Disease (the regimen and duration — essential) · Cardiology (echocardiography, heart failure, monitoring) · Cardiothoracic Surgery (early — surgical indications: heart failure, uncontrolled infection, emboli or a large vegetation, an abscess, prosthetic dehiscence) · Neurology (CNS emboli) · Addiction Medicine (IVDU) · Dental

• Diagnose rigorously: three sets of blood cultures before antibiotics, TTE then TEE, and application of the Modified Duke criteria; identify the organism (the duration and regimen depend on it)

• Empiric antibiotics (only after cultures are drawn; for the acutely ill or unstable patient — then narrow):

• • Native valve, acute disease, or IVDU: vancomycin IV (covering MRSA and most gram-positives), with gram-negative coverage per risk

• • Prosthetic valve: vancomycin plus gentamicin plus rifampin (per ID — biofilm, staph) pending cultures

• • Note: in a stable subacute presentation it is often best to await cultures before starting — coordinate with ID

• Targeted therapy (by organism and valve type — ID-directed; representative):

• • MSSA native → cefazolin 2 g IV every 8 hours (or nafcillin) for about 6 weeks; MRSA → vancomycin for about 6 weeks

• • Viridans strep (susceptible) → ceftriaxone or penicillin for about 4 weeks (native valve)

• • Enterococcus → ampicillin plus ceftriaxone (or plus gentamicin) for about 4–6 weeks

• • Prosthetic valve staph → add rifampin and gentamicin to the primary agent for at least 6 weeks

• Duration: prolonged IV — typically about 4–6 weeks (from the first negative culture for staph), and longer (≥6 weeks) for prosthetic valves; right-sided IVDU MSSA may be shorter (about 2 weeks) in selected uncomplicated cases per ID

• Step-down note: traditionally completed IV; selected stabilized left-sided IE may transition to an oral regimen after initial IV control per ID (the POET trial showed partial oral therapy non-inferior in stabilized, selected patients) — this is ID- and cardiology-directed, not routine; otherwise OPAT with a PICC completes the IV course

• Surgery (cardiothoracic — involve early for): heart failure from valve dysfunction, uncontrolled or persistent infection despite appropriate antibiotics, a perivalvular abscess or heart block, large mobile vegetations with recurrent emboli, prosthetic valve dehiscence or severe dysfunction, and fungal or highly resistant IE

• Repeat blood cultures every 24–48 hours to document clearance; treat heart failure, manage emboli, and provide addiction treatment and harm reduction (IVDU)

• PT/OT: per status, with neuro rehabilitation if there is an embolic stroke

• Trend: repeat blood cultures (clearance), the fever curve, a daily cardiac exam (a new murmur or heart failure), the ECG (a new block → an abscess), echocardiography as indicated, embolic surveillance, and end-organ function

• Escalation triggers: new heart failure → urgent surgery; persistent bacteremia despite therapy → TEE for an abscess or uncontrolled infection and surgery; new heart block → a root abscess → surgery; embolic events or a large vegetation → a surgical discussion; septic shock → ICU

• Discharge checklist: blood cultures cleared, clinically stable, and surgical questions addressed; the full prolonged regimen via OPAT/PICC (or a validated oral step-down) with the total duration and stop date specified; ID and cardiology follow-up with a repeat echo plan; dental care; addiction treatment linkage (IVDU); a clarified anticoagulation plan; return precautions for recurrent fever, new neurologic deficits, dyspnea or edema (heart failure), embolic symptoms, or line issues

Red Flags

• Heart failure from valve dysfunction → an urgent surgical indication

• A new heart block on ECG → a perivalvular root abscess → surgery

• Persistent bacteremia despite appropriate antibiotics → uncontrolled infection or an abscess → TEE and surgery

• A large mobile vegetation with recurrent emboli → a surgical discussion

• Prosthetic valve dehiscence or fungal IE → surgery

Senior IM Resident Pearls

• IE is a three-legged diagnosis. Cultures, echo, and Duke criteria together — draw three sets of blood cultures before antibiotics, get a TEE, and never let one negative test close the question.

• Call cardiac surgery early. Heart failure, an abscess with new heart block, a large mobile vegetation throwing emboli, or uncontrolled infection are all reasons valve surgery saves the patient.

• Treatment is a marathon. Four to six weeks IV, longer for prosthetic valves — and selected stabilized left-sided cases can finish orally under ID guidance per POET, but that's a deliberate decision, not a default.

• Persistent S. aureus bacteremia means echo. It's one of the strongest triggers to look for endocarditis — don't attribute it to a line without imaging the valves.

• Watch the ECG for new heart block. It signals a root abscess burrowing into the conduction system — a surgical emergency.

• Be careful with anticoagulation. Septic emboli can hemorrhage, so don't reflexively anticoagulate — coordinate with neurology and cardiology.

• Common mistake: treating S. aureus bacteremia as "just a line infection" and skipping the echo — that misses endocarditis and leads to undertreatment and relapse.

Infectious Disease — Viral Respiratory

116. Influenza

seasonal influenza · hypoxia · superimposed bacterial pneumonia · oseltamivir early (don't wait for testing if high suspicion + severe) · watch the secondary bacterial deterioration · Super Compact

Sx: abrupt onset fever, myalgias, headache, malaise, dry cough, sore throat, rhinorrhea; prostration out of proportion to exam · severe/complicated: dyspnea, hypoxia (primary viral pneumonia or ARDS) · secondary bacterial pneumonia: initial improvement then a "second hit" — recurrent fever, productive cough, new consolidation, worsening hypoxia (esp days 4–14) · (a flu patient who got better then suddenly worsens with new fever and consolidation has a superimposed bacterial pneumonia until proven otherwise — and S. aureus, including MRSA, is a feared cause)

Neg: denies missed secondary bacterial pneumonia (the biphasic deterioration — treat as CAP, add MRSA cover if necrotizing/severe) · denies delaying antiviral awaiting a test in severe/hospitalized disease · denies missed exacerbation of underlying disease (COPD/HF/asthma) · denies missed myocarditis/other complications

SHx: vaccination status (current season), time since symptom onset (antiviral timing), exposures/sick contacts/outbreak season, high-risk comorbidities (age extremes, pregnancy/postpartum, lung/heart disease, diabetes, immunocompromise, obesity, residents of care facilities), COPD/asthma

Etiology: influenza A or B virus → respiratory epithelial infection → systemic inflammatory illness; severe disease from primary viral pneumonia/ARDS · complications: secondary bacterial pneumonia (S. pneumoniae, S. aureus incl MRSA — can be necrotizing, H. influenzae), exacerbation of chronic lung/heart disease, myocarditis, myositis, encephalopathy · spread by droplets

RF: unvaccinated · age extremes · pregnancy · chronic lung/heart disease, diabetes · immunocompromise · obesity · care-facility residence

Data: influenza PCR/rapid molecular test (nasopharyngeal) + respiratory viral panel (covers COVID/RSV); SpO2 · CXR if hypoxic/lower-tract signs (viral pneumonia vs bacterial consolidation) · CBC, CMP; if secondary bacterial pneumonia suspected: blood + sputum cultures, procalcitonin (adjunct); troponin if chest pain/myocarditis concern

DDx: influenza · COVID-19 · other viral URI/pneumonia (RSV) · bacterial CAP · secondary bacterial pneumonia post-influenza · COPD/asthma exacerbation · myocarditis · PE

Home Meds: continue chronic meds; treat underlying COPD/asthma/HF; reconcile + renally dose oseltamivir (renal adjustment); VTE prophylaxis inpatient; antipyretics

Plan

CONSULT: Infectious Disease (severe/complicated, immunocompromised, antiviral resistance concerns) · Pulmonary/ICU (respiratory failure, ARDS, severe hypoxia) · Cardiology (myocarditis)

– ANTIVIRAL — start EARLY (greatest benefit <48 h of onset, but still give in hospitalized/severe/high-risk patients even if >48 h): oseltamivir 75 mg PO BID × 5 days (renally dosed; longer/higher-dose considered in severe/immunocompromised per ID); do NOT delay awaiting test results if clinical suspicion is high and the patient is hospitalized/severe — empiric oseltamivir is appropriate
– DROPLET PRECAUTIONS + supportive care: oxygen to target, fluids, antipyretics/analgesia, respiratory support (HFNC/NIV/intubation) and ICU for respiratory failure/ARDS
– TREAT SUPERIMPOSED BACTERIAL PNEUMONIA when suspected (biphasic worsening, new consolidation, high procalcitonin): treat as CAP — ceftriaxone 1–2 g IV q24h + azithromycin 500 mg IV/PO q24h (or levofloxacin 750 mg IV/PO daily); ADD vancomycin IV (MRSA) if severe/necrotizing pneumonia or MRSA risk (post-influenza S. aureus can be necrotizing); for HAP-setting/Pseudomonas risk escalate the beta-lactam to cefepime 2 g IV q8h (this formulary — replaces piperacillin-tazobactam)
– DON'T reflexively give antibiotics for uncomplicated influenza — reserve for documented/suspected bacterial co-infection
– STEP-DOWN + DURATION: oseltamivir is already oral (5-day course); if bacterial pneumonia treated: IV→PO once afebrile ~24–48 h, improving, SpO2 adequate, tolerating PO → oral CAP regimen (e.g. amoxicillin-clavulanate + macrolide, or levofloxacin 750 mg PO daily; add MRSA oral cover — linezolid or per culture — if MRSA confirmed); bacterial pneumonia duration ~5 days minimum (longer for S. aureus/necrotizing — see pneumonia card)
– PREVENTION: influenza vaccination (this and future seasons), post-exposure prophylaxis for high-risk contacts per guidance
– Treat influenza early and don't let the swab slow you down — in a sick, hospitalized, or high-risk patient with a compatible picture, start oseltamivir empirically, because the benefit is greatest early and still present even past 48 hours in severe disease. The trap is the biphasic course: a flu patient who improves and then takes a sudden turn for the worse — new fever, productive cough, fresh consolidation — has a secondary bacterial pneumonia, and post-influenza S. aureus can be necrotizing, so add MRSA coverage when the pneumonia looks severe. Otherwise, resist piling antibiotics onto uncomplicated flu.
– PT/OT: mobilization; pulmonary rehab if prolonged/ARDS
– Trend: fever curve (watch for a second rise = bacterial), oxygenation/work of breathing, cough/sputum, CXR if deteriorating, WBC/procalcitonin, response to antiviral
– Escalation triggers: respiratory failure/ARDS → ICU + respiratory support; secondary bacterial deterioration → add CAP/MRSA antibiotics + reimage; chest pain/arrhythmia/HF → evaluate myocarditis; immunocompromised/not improving → ID
– Discharge checklist: improving + stable oxygenation + tolerating PO; oseltamivir course (5 d) completed/continued + any bacterial-pneumonia oral regimen with duration/stop date specified; vaccination counseling for future seasons; household/high-risk-contact prophylaxis guidance; PCP follow-up; return precautions (recurrent/worsening fever, productive cough, dyspnea, chest pain, confusion)

116. Influenza

complete reference · hypoxia + superimposed bacterial pneumonia · early oseltamivir, watch the biphasic deterioration, MRSA cover for necrotizing pneumonia · Full Card

Symptoms / Associated Sx

• Abrupt onset of fever, myalgias, headache, malaise, dry cough, sore throat, and rhinorrhea, with prostration out of proportion to the exam

• Severe or complicated disease: dyspnea and hypoxia (primary viral pneumonia or ARDS)

• Secondary bacterial pneumonia: an initial improvement then a "second hit" — recurrent fever, productive cough, new consolidation, and worsening hypoxia (especially days 4–14)

• A flu patient who improved then suddenly worsens with new fever and consolidation has a superimposed bacterial pneumonia until proven otherwise — and S. aureus, including MRSA, is a feared cause

Neg

• Pt denies a missed secondary bacterial pneumonia (the biphasic deterioration — treat as CAP, adding MRSA coverage if necrotizing or severe)

• Pt denies delaying the antiviral while awaiting a test in severe or hospitalized disease

• Pt denies a missed exacerbation of underlying disease (COPD, heart failure, asthma) and a missed myocarditis or other complication

Social History (SHx)

• Vaccination status (the current season) and time since symptom onset (antiviral timing)

• Exposures, sick contacts, and the outbreak season

• High-risk comorbidities (extremes of age, pregnancy or postpartum, lung or heart disease, diabetes, immunocompromise, obesity, care-facility residence) and COPD or asthma

Main Etiology

• Influenza A or B virus infects the respiratory epithelium and produces a systemic inflammatory illness, with severe disease from primary viral pneumonia or ARDS

• Complications: secondary bacterial pneumonia (S. pneumoniae, S. aureus including MRSA — which can be necrotizing, and H. influenzae), exacerbation of chronic lung or heart disease, myocarditis, myositis, and encephalopathy

• Spread by droplets

RF

• Modifiable: vaccination status and obesity

• Non-modifiable: extremes of age, pregnancy, chronic lung or heart disease, diabetes, immunocompromise, and care-facility residence

Data

• Influenza PCR or a rapid molecular test (nasopharyngeal) with a respiratory viral panel (covering COVID and RSV); SpO2

• CXR if hypoxic or with lower-tract signs (viral pneumonia versus bacterial consolidation)

• CBC and CMP; if secondary bacterial pneumonia is suspected, blood and sputum cultures and procalcitonin (an adjunct); and troponin if there is chest pain or a myocarditis concern

DDx

Influenza · COVID-19 · other viral URI or pneumonia (RSV) · bacterial CAP · secondary bacterial pneumonia after influenza · a COPD or asthma exacerbation · myocarditis · PE

Home Meds

• Continue chronic medications and treat any underlying COPD, asthma, or heart failure

• Reconcile and renally dose oseltamivir (renal adjustment)

• Give VTE prophylaxis as an inpatient, with antipyretics

Plan

CONSULT: Infectious Disease (severe or complicated disease, immunocompromise, antiviral resistance concerns) · Pulmonary/ICU (respiratory failure, ARDS, severe hypoxia) · Cardiology (myocarditis)

• Antiviral — start early (the greatest benefit is within 48 hours of onset, but still give it to hospitalized, severe, or high-risk patients even beyond 48 hours): oseltamivir 75 mg PO twice daily for 5 days (renally dosed; a longer or higher dose is considered in severe or immunocompromised disease per ID); do not delay it awaiting test results if clinical suspicion is high and the patient is hospitalized or severe — empiric oseltamivir is appropriate

• Droplet precautions with supportive care: oxygen to target, fluids, antipyretics and analgesia, respiratory support (HFNC, NIV, intubation), and ICU for respiratory failure or ARDS

• Treat superimposed bacterial pneumonia when suspected (biphasic worsening, new consolidation, a high procalcitonin): treat as CAP — ceftriaxone 1–2 g IV every 24 hours plus azithromycin 500 mg IV/PO every 24 hours (or levofloxacin 750 mg IV/PO daily); add vancomycin IV (MRSA) if there is severe or necrotizing pneumonia or MRSA risk (post-influenza S. aureus can be necrotizing); for a HAP setting or Pseudomonas risk, escalate the beta-lactam to cefepime 2 g IV every 8 hours (this formulary — replacing piperacillin-tazobactam)

• Don't reflexively give antibiotics for uncomplicated influenza — reserve them for documented or suspected bacterial co-infection

• Step-down and duration: oseltamivir is already oral (a 5-day course); if bacterial pneumonia is treated, switch IV to PO once the patient is afebrile for about 24–48 hours, improving, with adequate SpO2 and tolerating oral intake → an oral CAP regimen (e.g. amoxicillin-clavulanate plus a macrolide, or levofloxacin 750 mg PO daily; add oral MRSA coverage — linezolid or per culture — if MRSA is confirmed); the bacterial pneumonia duration is about 5 days minimum (longer for S. aureus or necrotizing disease — see the pneumonia card)

• Prevention: influenza vaccination (this and future seasons) and post-exposure prophylaxis for high-risk contacts per guidance

• PT/OT: mobilization, with pulmonary rehabilitation if prolonged or ARDS

• Trend: the fever curve (watching for a second rise indicating bacterial infection), oxygenation and work of breathing, cough and sputum, the CXR if deteriorating, WBC and procalcitonin, and the response to the antiviral

• Escalation triggers: respiratory failure or ARDS → ICU and respiratory support; secondary bacterial deterioration → add CAP/MRSA antibiotics and re-image; chest pain, arrhythmia, or heart failure → evaluate for myocarditis; immunocompromised or not improving → ID

• Discharge checklist: improving with stable oxygenation and tolerating oral intake; the oseltamivir course (5 days) completed or continued, with any bacterial-pneumonia oral regimen and its duration and stop date specified; vaccination counseling for future seasons; household and high-risk-contact prophylaxis guidance; PCP follow-up; return precautions for recurrent or worsening fever, productive cough, dyspnea, chest pain, or confusion

Red Flags

• A biphasic course (improvement then sudden worsening) → secondary bacterial pneumonia; treat as CAP and re-image

• Severe or necrotizing pneumonia after influenza → S. aureus including MRSA; add vancomycin

• Hypoxia or respiratory failure → primary viral pneumonia or ARDS; ICU and respiratory support

• Chest pain, arrhythmia, or heart failure → influenza myocarditis

• Delaying the antiviral for test results in a severe or hospitalized patient → start oseltamivir empirically

Senior IM Resident Pearls

• Don't let the swab slow you down. In a sick, hospitalized, or high-risk patient with a compatible picture, start oseltamivir empirically — the benefit is greatest early and still present past 48 hours in severe disease.

• The biphasic course is the trap. A flu patient who improves then suddenly worsens has a secondary bacterial pneumonia until proven otherwise.

• Post-influenza S. aureus can be necrotizing. Add MRSA coverage with vancomycin when the secondary pneumonia looks severe.

• Resist antibiotics for uncomplicated flu. They do nothing for the virus — reserve them for documented or strongly suspected bacterial co-infection.

• The prostration is a clue. Influenza's abrupt onset and out-of-proportion malaise distinguish it from a gradual common cold.

• Vaccinate before discharge. The admission is a chance to address vaccination for this and future seasons and to advise high-risk contacts.

• Common mistake: attributing the "second fever" to the original flu and missing the bacterial pneumonia — a new productive cough and fresh consolidation demand antibiotics and re-imaging.

Infectious Disease — CNS

117. Meningitis

bacterial (emergency) vs viral · DON'T delay antibiotics for LP/CT · ceftriaxone + vancomycin + dexamethasone ± ampicillin (Listeria) · LP defines it · Super Compact

Sx: fever + headache + neck stiffness + altered mental status (classic triad often incomplete); photophobia, nausea/vomiting, seizures; petechial/purpuric rash → meningococcal (emergency) · meningismus (Kernig/Brudzinski) · viral (enteroviral): similar but usually less toxic, preserved mentation · (bacterial meningitis is a time-critical emergency — every hour of antibiotic delay worsens outcome, so give antibiotics + steroids FIRST and do the LP around them, never the reverse)

Neg: denies delaying antibiotics for CT or LP (treat first if any delay) · denies omitting dexamethasone before/with first antibiotic dose (pneumococcal benefit) · denies omitting ampicillin in Listeria-risk groups (>50, immunocompromised, pregnant) · denies missed contraindication to LP without CT (focal deficit, papilledema, immunocompromise, seizure) · denies missed encephalitis (HSV → acyclovir)

SHx: immune status (asplenia, complement deficiency, HIV, immunosuppression — encapsulated organisms/Listeria), age (>50 → Listeria), pregnancy (Listeria), recent neurosurgery/head trauma/CSF leak/shunt (staph/gram-neg, nosocomial), unvaccinated, close-contact/dorm/military exposure (meningococcal), sick contacts

Etiology: community bacterial: S. pneumoniae (most common adult), Neisseria meningitidis (young/clusters, rash), Listeria monocytogenes (>50, immunocompromised, pregnant), H. influenzae · nosocomial/post-neurosurgical: staph (incl MRSA), gram-negatives · viral: enteroviruses (most common viral), HSV (overlap with encephalitis) · spread by respiratory droplets (meningococcal/pneumococcal)

RF: immunocompromise/asplenia · age extremes · unvaccinated · close-contact settings · neurosurgery/CSF shunt/trauma · pregnancy (Listeria)

Data: LUMBAR PUNCTURE (the diagnostic test): opening pressure, cell count + differential, glucose (low in bacterial), protein (high in bacterial), Gram stain, culture, ± HSV PCR / enteroviral PCR / meningococcal-pneumococcal PCR · blood cultures BEFORE antibiotics (but don't delay abx) · CT head BEFORE LP only if: focal neuro deficit, papilledema, immunocompromise, new seizure, ↓consciousness (else LP without CT) · CBC, CMP, coags, lactate; bacterial CSF: ↑WBC (neutrophilic), ↓glucose, ↑protein; viral: ↑WBC (lymphocytic), normal glucose

DDx: bacterial meningitis · viral (aseptic) meningitis · HSV encephalitis (focal/AMS-predominant) · subarachnoid hemorrhage · brain abscess · fungal/TB meningitis (subacute, immunocompromised) · drug-induced aseptic meningitis · migraine/systemic infection

Home Meds: reconcile + renally dose abx; hold nothing that delays treatment; immunosuppression review with specialist; anticoagulation status for LP (correct coagulopathy/hold per risk before LP — but don't delay empiric abx)

Plan

CONSULT: Infectious Disease (regimen, duration, complex/nosocomial, immunocompromised) · Neurology (seizures, complications, encephalitis overlap) · Neurosurgery (shunt infection, hydrocephalus, abscess) · ICU (↓consciousness, septic, raised ICP) · Public Health (meningococcal — reporting + contact prophylaxis)

– TREAT IMMEDIATELY — do NOT wait for LP/CT (give within the first hour; sequence: blood cultures → dexamethasone → antibiotics → LP when safe):
  • DEXAMETHASONE 10 mg IV q6h × 4 days, given BEFORE or WITH the first antibiotic dose (reduces mortality/neuro sequelae in pneumococcal meningitis; continue if pneumococcal, stop if another organism)
  • Ceftriaxone 2 g IV q12h (S. pneumoniae, N. meningitidis, H. influenzae)
  • + Vancomycin IV (resistant pneumococcus — until susceptibility)
  • + Ampicillin 2 g IV q4h IF >50, immunocompromised, or pregnant (LISTERIA coverage — ceftriaxone does NOT cover Listeria)
  • Post-neurosurgical/shunt/nosocomial: vancomycin + cefepime 2 g IV q8h (this formulary — gram-negative incl Pseudomonas + MRSA; replaces piperacillin-tazobactam)
  • Penicillin/cephalosporin severe allergy: alternatives (e.g. moxifloxacin + vancomycin ± TMP-SMX for Listeria) — ID input
– ADD acyclovir 10 mg/kg IV q8h if encephalitis features (altered mentation, focal deficits, seizures — cover HSV until excluded; see encephalitis card)
– TARGET + DURATION (by organism, IV throughout — meningitis is treated IV, not stepped down to oral): S. pneumoniae ~10–14 days; N. meningitidis ~7 days; H. influenzae ~7 days; Listeria ≥21 days (ampicillin ± gentamicin); gram-negative ~21 days · viral (enteroviral) → supportive, usually self-limited; HSV → acyclovir 14–21 days
– DROPLET PRECAUTIONS for suspected meningococcal/Hib (until 24 h effective therapy) + chemoprophylaxis for close contacts of meningococcal disease (rifampin/ciprofloxacin/ceftriaxone) via public health
– Supportive: manage raised ICP/seizures, fluids/electrolytes (watch SIADH), antipyretics, ICU for depressed consciousness/instability
– The whole game in bacterial meningitis is speed: blood cultures, then dexamethasone, then antibiotics — within the first hour — and the LP fits around that, not before it. The only reason to CT before tapping is a focal deficit, papilledema, immunocompromise, a new seizure, or depressed consciousness; otherwise the scan just wastes time. Two coverage points save lives: dexamethasone goes in with (or just before) the first dose for the pneumococcal benefit, and anyone over 50, pregnant, or immunocompromised needs ampicillin added because ceftriaxone misses Listeria. Meningitis is treated IV start to finish — there's no oral step-down here.
– PT/OT: neuro rehab if deficits/sequelae
– Trend: mental status/GCS, neuro exam, fever, CSF/culture results (narrow therapy), seizures, ICP signs, sodium (SIADH), hearing (pneumococcal sequela)
– Escalation triggers: depressed consciousness/raised ICP/status epilepticus → ICU + neuro/neurosurgery; hydrocephalus/shunt issue → neurosurgery; no improvement → reconsider organism (resistant, TB/fungal, encephalitis) + repeat LP + ID; septic shock → ICU
– Discharge checklist: completing the full organism-specific IV course (OPAT/PICC if needed) — total duration/stop date specified; ID follow-up; audiology evaluation (pneumococcal hearing loss); neuro follow-up for sequelae; public-health reporting + contact prophylaxis completed (meningococcal); vaccination counseling (pneumococcal/meningococcal as indicated, esp asplenia); return precautions (recurrent fever, headache, neck stiffness, confusion, seizures, new deficits)

117. Meningitis

complete reference · bacterial (emergency) + viral · antibiotics + dexamethasone first, LP around them, ampicillin for Listeria, IV throughout · Full Card

Symptoms / Associated Sx

• Fever, headache, neck stiffness, and altered mental status (the classic triad is often incomplete), with photophobia, nausea and vomiting, and seizures

• A petechial or purpuric rash points to meningococcal disease (an emergency)

• Meningismus (Kernig and Brudzinski signs)

• Viral (enteroviral) disease is similar but usually less toxic, with preserved mentation

• Bacterial meningitis is a time-critical emergency — every hour of antibiotic delay worsens the outcome, so give antibiotics and steroids first and do the LP around them, never the reverse

Neg

• Pt denies delaying antibiotics for a CT or LP (treat first if there is any delay)

• Pt denies omitting dexamethasone before or with the first antibiotic dose (the pneumococcal benefit) and omitting ampicillin in Listeria-risk groups (over 50, immunocompromised, pregnant)

• Pt denies a missed contraindication to LP without CT (a focal deficit, papilledema, immunocompromise, a seizure) and a missed encephalitis (HSV → acyclovir)

Social History (SHx)

• Immune status (asplenia, complement deficiency, HIV, immunosuppression — encapsulated organisms and Listeria), age (over 50 → Listeria), and pregnancy (Listeria)

• Recent neurosurgery, head trauma, a CSF leak, or a shunt (staph and gram-negatives, nosocomial)

• Being unvaccinated, close-contact, dorm, or military exposure (meningococcal), and sick contacts

Main Etiology

• Community bacterial disease: S. pneumoniae (the most common in adults), Neisseria meningitidis (the young, clusters, a rash), Listeria monocytogenes (over 50, immunocompromised, pregnant), and H. influenzae

• Nosocomial or post-neurosurgical disease: staph (including MRSA) and gram-negatives

• Viral disease: enteroviruses (the most common viral cause) and HSV (overlapping with encephalitis)

• Spread by respiratory droplets (meningococcal, pneumococcal)

RF

• Modifiable: vaccination status and a CSF shunt

• Non-modifiable: immunocompromise or asplenia, extremes of age, close-contact settings, neurosurgery or trauma, and pregnancy (Listeria)

Data

• Lumbar puncture (the diagnostic test): opening pressure, cell count and differential, glucose (low in bacterial disease), protein (high in bacterial disease), Gram stain, culture, with HSV PCR, enteroviral PCR, or meningococcal-pneumococcal PCR

• Blood cultures before antibiotics (but don't delay antibiotics)

• CT head before LP only if there is a focal neurologic deficit, papilledema, immunocompromise, a new seizure, or depressed consciousness (otherwise LP without CT)

• CBC, CMP, coagulation studies, and lactate; bacterial CSF shows an elevated neutrophilic WBC, low glucose, and high protein, while viral CSF shows an elevated lymphocytic WBC and normal glucose

DDx

Bacterial meningitis · viral (aseptic) meningitis · HSV encephalitis (focal or AMS-predominant) · subarachnoid hemorrhage · a brain abscess · fungal or TB meningitis (subacute, immunocompromised) · drug-induced aseptic meningitis · migraine or systemic infection

Home Meds

• Reconcile and renally dose antibiotics; hold nothing that delays treatment

• Review immunosuppression with the specialist

• Check anticoagulation status for the LP (correct coagulopathy or hold per risk before the LP — but don't delay empiric antibiotics)

Plan

CONSULT: Infectious Disease (regimen, duration, complex or nosocomial disease, immunocompromise) · Neurology (seizures, complications, encephalitis overlap) · Neurosurgery (shunt infection, hydrocephalus, abscess) · ICU (depressed consciousness, sepsis, raised ICP) · Public Health (meningococcal — reporting and contact prophylaxis)

• Treat immediately — do not wait for the LP or CT (give within the first hour; the sequence is blood cultures → dexamethasone → antibiotics → LP when safe):

• • Dexamethasone 10 mg IV every 6 hours for 4 days, given before or with the first antibiotic dose (it reduces mortality and neurologic sequelae in pneumococcal meningitis; continue if pneumococcal, stop if another organism)

• • Ceftriaxone 2 g IV every 12 hours (S. pneumoniae, N. meningitidis, H. influenzae)

• • Plus vancomycin IV (resistant pneumococcus — until susceptibility)

• • Plus ampicillin 2 g IV every 4 hours if over 50, immunocompromised, or pregnant (Listeria coverage — ceftriaxone does not cover Listeria)

• • Post-neurosurgical, shunt, or nosocomial disease: vancomycin plus cefepime 2 g IV every 8 hours (this formulary — gram-negatives including Pseudomonas plus MRSA; replacing piperacillin-tazobactam)

• • Severe penicillin/cephalosporin allergy: alternatives (e.g. moxifloxacin plus vancomycin, with TMP-SMX for Listeria) — ID input

• Add acyclovir 10 mg/kg IV every 8 hours if there are encephalitis features (altered mentation, focal deficits, seizures — covering HSV until excluded; see the encephalitis card)

• Target and duration (by organism, IV throughout — meningitis is treated IV, not stepped down to oral): S. pneumoniae about 10–14 days; N. meningitidis about 7 days; H. influenzae about 7 days; Listeria at least 21 days (ampicillin, with gentamicin); gram-negative disease about 21 days; viral (enteroviral) disease is supportive and usually self-limited; HSV → acyclovir for 14–21 days

• Droplet precautions for suspected meningococcal or Hib disease (until 24 hours of effective therapy) plus chemoprophylaxis for close contacts of meningococcal disease (rifampin, ciprofloxacin, or ceftriaxone) via public health

• Supportive care: manage raised ICP and seizures, fluids and electrolytes (watching for SIADH), antipyretics, and ICU for depressed consciousness or instability

• PT/OT: neuro rehabilitation if there are deficits or sequelae

• Trend: mental status and GCS, the neurologic exam, fever, CSF and culture results (to narrow therapy), seizures, signs of raised ICP, sodium (SIADH), and hearing (a pneumococcal sequela)

• Escalation triggers: depressed consciousness, raised ICP, or status epilepticus → ICU with neurology and neurosurgery; hydrocephalus or a shunt issue → neurosurgery; no improvement → reconsider the organism (resistant, TB, fungal, encephalitis), repeat the LP, and ID; septic shock → ICU

• Discharge checklist: completing the full organism-specific IV course (OPAT/PICC if needed) with the total duration and stop date specified; ID follow-up; an audiology evaluation (pneumococcal hearing loss); neuro follow-up for sequelae; public-health reporting and contact prophylaxis completed (meningococcal); vaccination counseling (pneumococcal and meningococcal as indicated, especially in asplenia); return precautions for recurrent fever, headache, neck stiffness, confusion, seizures, or new deficits

Red Flags

• Any delay in antibiotics for a CT or LP → treat first; every hour of delay worsens the outcome

• A petechial or purpuric rash → meningococcal disease; droplet precautions and contact prophylaxis

• Over 50, pregnant, or immunocompromised → add ampicillin, as ceftriaxone misses Listeria

• Focal deficit, papilledema, immunocompromise, seizure, or depressed consciousness → CT before LP (but still treat first)

• Altered mentation or focal deficits → consider HSV encephalitis and add acyclovir

Senior IM Resident Pearls

• Speed is the whole game. Blood cultures, then dexamethasone, then antibiotics — within the first hour — with the LP fitting around that, not before it.

• CT before LP only for specific reasons. A focal deficit, papilledema, immunocompromise, a new seizure, or depressed consciousness — otherwise the scan just wastes time.

• Dexamethasone goes in with the first dose. The pneumococcal mortality and hearing-loss benefit depends on giving it before or with the antibiotic, not after.

• Add ampicillin for Listeria. Anyone over 50, pregnant, or immunocompromised needs it, because ceftriaxone has no Listeria activity.

• Meningitis is treated IV start to finish. There's no oral step-down — plan OPAT for the organism-specific course rather than switching to pills.

• Arrange audiology. Hearing loss is a common pneumococcal sequela that's easy to forget at discharge.

• Common mistake: sending the patient to CT and then to LP before any antibiotics — the right move is to treat empirically the moment bacterial meningitis is suspected and let the workup follow.

Infectious Disease — CNS

118. Encephalitis

HSV · other viral causes · EMPIRIC IV acyclovir IMMEDIATELY on suspicion — don't wait for PCR · MRI + CSF HSV PCR + EEG · autoimmune on the differential · Super Compact

Sx: altered mental status / encephalopathy + fever ± focal neuro deficits, seizures, behavioral/personality change, aphasia, memory disturbance, hallucinations · HSV: often temporal-lobe features (aphasia, focal seizures, behavioral change) · (vs meningitis: encephalitis = brain parenchyma → AMS/focal signs dominate; meningitis = meninges → meningismus dominates; overlap common) · (fever + new altered mentation or focal/behavioral change = HSV encephalitis until excluded — and because untreated HSV encephalitis is devastating, you start acyclovir on suspicion, not on confirmation)

Neg: denies delaying empiric acyclovir for PCR/MRI (treat first — delay drives mortality + disability) · denies stopping acyclovir on a single early-negative HSV PCR (can be falsely negative very early — repeat) · denies missed bacterial meningitis (cover concurrently if unclear) · denies missed autoimmune/limbic encephalitis (paraneoplastic/anti-NMDA — immunotherapy) · denies missed mass/abscess/stroke mimics

SHx: immune status (immunocompromised → broader: CMV, VZV, fungal, Toxoplasma, PML), HIV status, vaccination, travel/season/exposures (arboviruses — West Nile, mosquito; tick exposure), animal/bat exposure (rabies), recent viral illness (post-infectious ADEM), malignancy/autoimmune history (limbic/paraneoplastic)

Etiology: HSV-1 (the most important treatable cause — temporal lobe, hemorrhagic necrosis), also VZV, enteroviruses, arboviruses (West Nile), CMV/others in immunocompromised · autoimmune/paraneoplastic encephalitis (anti-NMDA receptor, limbic) increasingly recognized · post-infectious (ADEM) · parenchymal brain inflammation → neuronal dysfunction/edema/seizures

RF: immunocompromise (broader pathogens) · age extremes · arbovirus exposure (season/region) · animal/tick/mosquito exposure · malignancy/autoimmune (autoimmune encephalitis)

Data: LP: CSF HSV PCR (key test — may be negative in first 24–72 h, repeat if high suspicion), cell count (lymphocytic ± RBCs in HSV), glucose, protein, culture, enteroviral/VZV/other PCR, autoimmune antibody panel · MRI brain (temporal-lobe involvement in HSV — most sensitive) · EEG (focal temporal epileptiform/seizures) · CBC, CMP, blood cultures, HIV test; CT if LP delayed/contraindicated; paraneoplastic workup if autoimmune suspected

DDx: HSV encephalitis · other viral encephalitis (VZV, arbovirus, enterovirus) · autoimmune/limbic/anti-NMDA encephalitis · bacterial meningitis/meningoencephalitis · brain abscess/mass · stroke · toxic-metabolic encephalopathy · status epilepticus/postictal · CNS vasculitis · ADEM

Home Meds: reconcile + renally dose acyclovir (nephrotoxic — aggressive IV hydration, monitor renal function/crystalluria); hold nephrotoxins; immunosuppression review; anticoagulation status for LP

Plan

CONSULT: Neurology (diagnosis, seizures, autoimmune workup, EEG) · Infectious Disease (antiviral, immunocompromised, atypical pathogens) · ICU (depressed consciousness, status epilepticus, cerebral edema) · Neurosurgery (raised ICP/mass)

– START EMPIRIC IV ACYCLOVIR IMMEDIATELY on clinical suspicion — do NOT wait for PCR or MRI: acyclovir 10 mg/kg IV q8h (dose by ideal body weight; renally adjusted) with aggressive IV hydration (prevent nephrotoxicity/crystal nephropathy) — early treatment is the single biggest determinant of outcome in HSV encephalitis
– COVER bacterial meningitis concurrently if the picture is unclear (fever + AMS): add ceftriaxone 2 g IV q12h + vancomycin + dexamethasone ± ampicillin (Listeria risk) until bacterial meningitis excluded (see meningitis card)
– CONFIRM + CHARACTERIZE: LP with HSV PCR (repeat in 3–7 days if initially negative but suspicion remains — early false-negatives occur), MRI brain, EEG; HIV test; broaden per host/exposure (VZV → acyclovir continues; CMV in immunocompromised → ganciclovir; arbovirus → supportive)
– DURATION: confirmed HSV encephalitis → IV acyclovir 14–21 days (treated IV — not stepped down to oral for HSV encephalitis; some confirm CSF PCR clearance before stopping per ID); if HSV excluded + alternative found, tailor accordingly; if all workup negative + low suspicion, acyclovir may be stopped per ID/neuro
– CONSIDER AUTOIMMUNE encephalitis (subacute, psychiatric/behavioral, anti-NMDA, refractory seizures, no infection found) → autoimmune antibody panel + paraneoplastic/tumor workup → immunotherapy (steroids, IVIG, plasma exchange) per neurology
– Supportive/seizure + ICP management: antiepileptics for seizures, manage cerebral edema/raised ICP, fluids/electrolytes (SIADH), ICU for depressed consciousness/status/edema
– The reflex that defines this card: fever plus new altered mentation or focal/behavioral change means start IV acyclovir now, before the PCR and before the MRI — because the outcome of HSV encephalitis hinges on how fast you treat, and waiting for confirmation costs brain. Don't be fooled by an early-negative HSV PCR either; it can be falsely negative in the first day or two, so if suspicion is high you repeat it and keep treating. And when the workup comes back clean but the patient has subacute psychiatric symptoms and refractory seizures, pivot to autoimmune encephalitis — anti-NMDA disease responds to immunotherapy, not antivirals.
– PT/OT: neuro rehab (cognitive/functional deficits common after encephalitis)
– Trend: mental status/GCS, neuro exam, seizures/EEG, renal function (acyclovir), repeat HSV PCR if indicated, MRI evolution, response to therapy
– Escalation triggers: depressed consciousness/cerebral edema/status epilepticus → ICU + neuro; raised ICP/mass effect → neurosurgery; no improvement + negative HSV → reconsider autoimmune/alternative (immunotherapy trial per neuro); immunocompromised/atypical → ID broaden
– Discharge checklist: antiviral course defined (HSV → complete IV 14–21 d, OPAT if needed) with total duration/stop date specified; neuro + ID follow-up; cognitive/neuropsych rehab arranged (sequelae common); seizure-management plan + antiepileptics; autoimmune follow-up/tumor surveillance if relevant; return precautions (worsening confusion, seizures, new deficits, fever, behavioral change)

118. Encephalitis

complete reference · HSV + other viral causes · empiric IV acyclovir on suspicion, repeat PCR if early-negative, autoimmune on the differential · Full Card

Symptoms / Associated Sx

• Altered mental status or encephalopathy with fever, with or without focal neurologic deficits, seizures, behavioral or personality change, aphasia, memory disturbance, and hallucinations

• HSV often produces temporal-lobe features (aphasia, focal seizures, behavioral change)

• Versus meningitis: encephalitis is brain parenchyma, so altered mentation and focal signs dominate; meningitis is the meninges, so meningismus dominates, though overlap is common

• Fever with new altered mentation or focal/behavioral change is HSV encephalitis until excluded — and because untreated HSV encephalitis is devastating, you start acyclovir on suspicion, not on confirmation

Neg

• Pt denies delaying empiric acyclovir for PCR or MRI (treat first — delay drives mortality and disability)

• Pt denies stopping acyclovir on a single early-negative HSV PCR (it can be falsely negative very early — repeat it) and a missed bacterial meningitis (cover concurrently if unclear)

• Pt denies a missed autoimmune or limbic encephalitis (paraneoplastic, anti-NMDA — immunotherapy) and missed mass, abscess, or stroke mimics

Social History (SHx)

• Immune status (immunocompromised → a broader differential: CMV, VZV, fungal, Toxoplasma, PML) and HIV status

• Vaccination, travel, season, and exposures (arboviruses such as West Nile from mosquitoes; tick exposure), and animal or bat exposure (rabies)

• Recent viral illness (post-infectious ADEM) and a malignancy or autoimmune history (limbic or paraneoplastic disease)

Main Etiology

• HSV-1 (the most important treatable cause — temporal lobe, hemorrhagic necrosis), also VZV, enteroviruses, arboviruses (West Nile), and CMV and others in the immunocompromised

• Autoimmune and paraneoplastic encephalitis (anti-NMDA receptor, limbic) is increasingly recognized

• Post-infectious ADEM

• Parenchymal brain inflammation causes neuronal dysfunction, edema, and seizures

RF

• Modifiable: arbovirus exposure (season, region) and animal, tick, or mosquito exposure

• Non-modifiable: immunocompromise (broader pathogens), extremes of age, and malignancy or autoimmune disease (autoimmune encephalitis)

Data

• LP: CSF HSV PCR (the key test — may be negative in the first 24–72 hours, so repeat if suspicion is high), cell count (lymphocytic, with RBCs in HSV), glucose, protein, culture, enteroviral/VZV/other PCR, and an autoimmune antibody panel

• MRI brain (temporal-lobe involvement in HSV — the most sensitive imaging)

• EEG (focal temporal epileptiform activity or seizures)

• CBC, CMP, blood cultures, and an HIV test; CT if the LP is delayed or contraindicated; and a paraneoplastic workup if autoimmune disease is suspected

DDx

HSV encephalitis · other viral encephalitis (VZV, arbovirus, enterovirus) · autoimmune, limbic, or anti-NMDA encephalitis · bacterial meningitis or meningoencephalitis · a brain abscess or mass · stroke · toxic-metabolic encephalopathy · status epilepticus or a postictal state · CNS vasculitis · ADEM

Home Meds

• Reconcile and renally dose acyclovir (it is nephrotoxic — give aggressive IV hydration and monitor renal function and crystalluria)

• Hold nephrotoxins; review immunosuppression

• Check anticoagulation status for the LP

Plan

CONSULT: Neurology (diagnosis, seizures, autoimmune workup, EEG) · Infectious Disease (antiviral therapy, immunocompromise, atypical pathogens) · ICU (depressed consciousness, status epilepticus, cerebral edema) · Neurosurgery (raised ICP or a mass)

• Start empiric IV acyclovir immediately on clinical suspicion — do not wait for PCR or MRI: acyclovir 10 mg/kg IV every 8 hours (dosed by ideal body weight, renally adjusted) with aggressive IV hydration (to prevent nephrotoxicity and crystal nephropathy) — early treatment is the single biggest determinant of outcome in HSV encephalitis

• Cover bacterial meningitis concurrently if the picture is unclear (fever plus altered mental status): add ceftriaxone 2 g IV every 12 hours plus vancomycin and dexamethasone, with ampicillin if there is Listeria risk, until bacterial meningitis is excluded (see the meningitis card)

• Confirm and characterize: LP with HSV PCR (repeated in 3–7 days if initially negative but suspicion remains — early false-negatives occur), MRI brain, and EEG; an HIV test; and broaden per host and exposure (VZV → continue acyclovir; CMV in the immunocompromised → ganciclovir; arbovirus → supportive care)

• Duration: confirmed HSV encephalitis → IV acyclovir for 14–21 days (treated IV — not stepped down to oral for HSV encephalitis; some confirm CSF PCR clearance before stopping per ID); if HSV is excluded and an alternative is found, tailor accordingly; if all workup is negative with low suspicion, acyclovir may be stopped per ID and neurology

• Consider autoimmune encephalitis (subacute, psychiatric or behavioral, anti-NMDA, refractory seizures, no infection found) → an autoimmune antibody panel and a paraneoplastic/tumor workup → immunotherapy (steroids, IVIG, plasma exchange) per neurology

• Supportive, seizure, and ICP management: antiepileptics for seizures, management of cerebral edema and raised ICP, fluids and electrolytes (SIADH), and ICU for depressed consciousness, status, or edema

• PT/OT: neuro rehabilitation (cognitive and functional deficits are common after encephalitis)

• Trend: mental status and GCS, the neurologic exam, seizures and EEG, renal function (acyclovir), a repeat HSV PCR if indicated, MRI evolution, and the response to therapy

• Escalation triggers: depressed consciousness, cerebral edema, or status epilepticus → ICU and neurology; raised ICP or mass effect → neurosurgery; no improvement with a negative HSV PCR → reconsider autoimmune or alternative causes (an immunotherapy trial per neurology); immunocompromised or atypical disease → ID and broaden

• Discharge checklist: the antiviral course defined (HSV → complete the IV 14–21 days, OPAT if needed) with the total duration and stop date specified; neuro and ID follow-up; cognitive and neuropsychological rehabilitation arranged (sequelae are common); a seizure-management plan with antiepileptics; autoimmune follow-up and tumor surveillance if relevant; return precautions for worsening confusion, seizures, new deficits, fever, or behavioral change

Red Flags

• Any delay in empiric acyclovir for PCR or MRI → treat first; delay drives mortality and disability

• An early-negative HSV PCR with high suspicion → can be falsely negative; repeat it and keep treating

• Depressed consciousness, cerebral edema, or status epilepticus → ICU

• Subacute psychiatric symptoms with refractory seizures and no infection → autoimmune (anti-NMDA) encephalitis; immunotherapy

• Unclear fever plus altered mental status → cover bacterial meningitis concurrently

Senior IM Resident Pearls

• Fever plus new altered mentation means acyclovir now. Start IV acyclovir before the PCR and before the MRI — the outcome of HSV encephalitis hinges on how fast you treat.

• Don't trust an early-negative HSV PCR. It can be falsely negative in the first day or two, so if suspicion is high, repeat it and continue treating.

• Hydrate for the acyclovir. It's nephrotoxic and crystallizes in the tubules — aggressive IV fluids and renal monitoring prevent the AKI.

• Pivot to autoimmune when the workup is clean. Subacute psychiatric symptoms with refractory seizures and no infection suggest anti-NMDA disease that responds to immunotherapy.

• Cover bacterial meningitis when it's unclear. Fever plus altered mental status often warrants concurrent antibiotics and dexamethasone until the LP sorts it out.

• Expect sequelae. Cognitive and functional deficits are common after encephalitis — arrange neuropsychological rehabilitation early.

• Common mistake: waiting for the HSV PCR result before starting acyclovir — that delay is exactly what worsens the outcome the drug is meant to prevent.

Infectious Disease — Skin/Soft Tissue

119. Skin and Soft Tissue Abscess

cutaneous abscess/furuncle/carbuncle · MRSA · recurrent abscesses · I&D is the PRIMARY treatment · antibiotics are adjunctive · decolonize for recurrence · Super Compact

Sx: localized fluctuant, tender, erythematous, warm swelling ± central pointing/spontaneous drainage; surrounding cellulitis; furuncle (single hair follicle), carbuncle (coalesced); ± fever/systemic signs in larger/multiple/immunocompromised · (an abscess is a drainage problem, not primarily an antibiotic problem — the fluctuant collection needs to be opened, and the pus you drain is the culture that guides any antibiotic)

Neg: denies treating with antibiotics instead of draining (I&D is the definitive treatment — antibiotics alone won't cure a walled-off abscess) · denies missed deeper/necrotizing infection (pain out of proportion, systemic toxicity → emergency) · denies missed special sites (perirectal/perianal, hand, facial "danger triangle", deep neck → specialist) · denies missed underlying cause in recurrent disease (decolonization, diabetes, immunodeficiency, hidradenitis)

SHx: prior abscesses/MRSA (recurrence + decolonization), IVDU (injection abscesses), diabetes/immunocompromise, close-contact/household MRSA, athletic/skin-trauma exposure, hidradenitis suppurativa (recurrent specific sites), poor hygiene/crowding

Etiology: S. aureus — community-associated MRSA is a leading cause of skin abscesses; also MSSA, streptococci; polymicrobial/anaerobic at special sites (perirectal, genital) · purulent collection walled off by host response → needs mechanical drainage; biofilm/colonization (nares, skin) drives recurrence

RF: prior MRSA/abscess · IVDU · diabetes/immunocompromise · skin trauma/athletic contact · household MRSA · hidradenitis suppurativa · crowding/hygiene

Data: clinical diagnosis; obtain culture of purulent drainage at I&D (guides antibiotics + tracks MRSA) · bedside ultrasound to confirm a drainable collection (vs cellulitis without fluid) if uncertain · CBC/labs + blood cultures only if systemically ill/immunocompromised · imaging (CT/MRI) for deep/special-site/complex abscesses; glucose/A1c if diabetic; consider HIV/immune workup in recurrent/atypical

DDx: cutaneous abscess · cellulitis without abscess (no drainable fluid) · infected epidermoid cyst · hidradenitis suppurativa · necrotizing infection (emergency) · septic bursitis · perirectal/Bartholin/other site-specific abscess · hematoma · neoplasm

Home Meds: reconcile + renally dose any abx; optimize diabetes; analgesia; review for immunosuppression in recurrent disease

Plan

CONSULT: Surgery (large/deep/complex abscess, special sites — perirectal/deep neck/hand, inadequate bedside drainage) · Infectious Disease (recurrent, immunocompromised, treatment failure, decolonization) · Dermatology (hidradenitis suppurativa) · Surgery/Colorectal (perirectal)

– INCISION & DRAINAGE is the primary, definitive treatment: adequately incise, drain pus, break loculations, irrigate; send drainage for culture & susceptibility; packing or loop drainage as appropriate; complex/deep/special-site → surgery
– ANTIBIOTICS are ADJUNCTIVE (I&D alone cures many simple abscesses) — add antibiotics (with MRSA coverage) when: surrounding cellulitis, systemic signs (fever/SIRS), large or multiple abscesses, immunocompromise/diabetes, high-risk location (face/hands/genitalia), failure of I&D alone, very young/old, or inability to fully drain (evidence: adjunctive antibiotics improve cure for moderate abscesses)
– EMPIRIC ORAL ANTIBIOTICS (MRSA coverage, outpatient/ward): TMP-SMX DS 1–2 tabs PO q12h, OR doxycycline 100 mg PO q12h, OR clindamycin 300–450 mg PO q6–8h (also covers strep; watch C. diff/resistance)
– SEVERE/SYSTEMIC (IV): vancomycin IV (MRSA) ± gram-negative/anaerobic coverage for special sites (perirectal/genital → add cefepime 2 g IV q8h + metronidazole 500 mg IV q8h, this formulary's gram-negative + anaerobe pairing replacing piperacillin-tazobactam)
– STEP-DOWN + DURATION: IV→PO once drained + improving + afebrile + tolerating PO → MRSA-active oral agent above; duration short — ~5–7 days when antibiotics are indicated (many simple drained abscesses need none); tailor to culture
– RECURRENT ABSCESSES → DECOLONIZATION + workup: intranasal mupirocin BID × 5 days, chlorhexidine skin washes, hygiene measures (launder linens, avoid sharing); treat household contacts if recurrent; evaluate for diabetes/immunodeficiency/HIV/hidradenitis; ID involvement
– Internalize that an abscess is plumbing, not pharmacology: the cure is opening it and letting it drain, and a simple drained abscess in a well patient often needs no antibiotics at all. Add antibiotics with MRSA coverage when there's surrounding cellulitis, systemic signs, multiple or large abscesses, or an immunocompromised host — and the drainage you send is the culture that confirms MRSA. For the patient who keeps coming back, stop just draining and start decolonizing — mupirocin and chlorhexidine — and look for the reason (diabetes, hidradenitis, household MRSA). The course, when antibiotics are needed, is short.
– PT/OT: rarely needed; wound care for packing/dressing changes
– Trend: wound/drainage, surrounding erythema, fever/systemic signs, response, culture/susceptibility (confirm MRSA-active agent), glucose if diabetic
– Escalation triggers: necrotizing features/systemic toxicity → emergent surgery; inadequate drainage/persistent collection → repeat I&D/surgery + imaging; failure to improve → reassess organism/coverage + ID; special-site/deep → surgical specialty
– Discharge checklist: abscess adequately drained + improving; oral regimen (if indicated) + short duration/stop date specified, MRSA-active; wound-care/packing-change plan; recurrence prevention: decolonization regimen + hygiene + underlying-cause workup if recurrent; culture follow-up; PCP/ID/surgery follow-up; return precautions (spreading redness, increasing pain/swelling, fever, re-accumulation, drainage changes)

119. Skin and Soft Tissue Abscess

complete reference · MRSA + recurrent abscesses · I&D primary, adjunctive MRSA antibiotics by criteria, decolonization for recurrence · Full Card

Symptoms / Associated Sx

• A localized fluctuant, tender, erythematous, warm swelling, with or without central pointing or spontaneous drainage; surrounding cellulitis

• A furuncle (a single hair follicle) or carbuncle (coalesced furuncles)

• Fever or systemic signs with larger, multiple, or immunocompromised disease

• An abscess is a drainage problem, not primarily an antibiotic problem — the fluctuant collection needs to be opened, and the pus drained is the culture that guides any antibiotic

Neg

• Pt denies treating with antibiotics instead of draining (I&D is the definitive treatment — antibiotics alone won't cure a walled-off abscess)

• Pt denies a missed deeper or necrotizing infection (pain out of proportion, systemic toxicity → an emergency) and missed special sites (perirectal or perianal, hand, the facial "danger triangle," deep neck → a specialist)

• Pt denies a missed underlying cause in recurrent disease (decolonization, diabetes, immunodeficiency, hidradenitis)

Social History (SHx)

• Prior abscesses or MRSA (recurrence and decolonization), IV drug use (injection abscesses), and diabetes or immunocompromise

• Close-contact or household MRSA, and athletic or skin-trauma exposure

• Hidradenitis suppurativa (recurrent at specific sites) and crowding or poor hygiene

Main Etiology

• S. aureus — community-associated MRSA is a leading cause of skin abscesses; also MSSA and streptococci

• Polymicrobial or anaerobic at special sites (perirectal, genital)

• A purulent collection walled off by the host response needs mechanical drainage; biofilm and colonization (nares, skin) drive recurrence

RF

• Modifiable: skin trauma or athletic contact, household MRSA, and hygiene or crowding

• Non-modifiable: prior MRSA or abscess, IV drug use, diabetes or immunocompromise, and hidradenitis suppurativa

Data

• A clinical diagnosis; obtain a culture of purulent drainage at I&D (guiding antibiotics and tracking MRSA)

• Bedside ultrasound to confirm a drainable collection (versus cellulitis without fluid) if uncertain

• CBC, other labs, and blood cultures only if systemically ill or immunocompromised; imaging (CT/MRI) for deep, special-site, or complex abscesses; glucose/A1c if diabetic; and consider an HIV or immune workup in recurrent or atypical disease

DDx

A cutaneous abscess · cellulitis without an abscess (no drainable fluid) · an infected epidermoid cyst · hidradenitis suppurativa · necrotizing infection (an emergency) · septic bursitis · a perirectal, Bartholin, or other site-specific abscess · a hematoma · a neoplasm

Home Meds

• Reconcile and renally dose any antibiotics

• Optimize diabetes and provide analgesia

• Review for immunosuppression in recurrent disease

Plan

CONSULT: Surgery (a large, deep, or complex abscess, special sites — perirectal, deep neck, hand — or inadequate bedside drainage) · Infectious Disease (recurrent disease, immunocompromise, treatment failure, decolonization) · Dermatology (hidradenitis suppurativa) · Surgery/Colorectal (perirectal disease)

• Incision and drainage is the primary, definitive treatment: adequately incise, drain the pus, break loculations, and irrigate; send the drainage for culture and susceptibility; use packing or loop drainage as appropriate; complex, deep, or special-site disease → surgery

• Antibiotics are adjunctive (I&D alone cures many simple abscesses) — add antibiotics (with MRSA coverage) when there is surrounding cellulitis, systemic signs (fever, SIRS), a large or multiple abscesses, immunocompromise or diabetes, a high-risk location (face, hands, genitalia), failure of I&D alone, very young or old age, or an inability to fully drain (adjunctive antibiotics improve cure for moderate abscesses)

• Empiric oral antibiotics (MRSA coverage, outpatient or ward): TMP-SMX DS 1–2 tablets PO every 12 hours, or doxycycline 100 mg PO every 12 hours, or clindamycin 300–450 mg PO every 6–8 hours (which also covers strep; watch for C. difficile and resistance)

• Severe or systemic disease (IV): vancomycin IV (MRSA), with gram-negative and anaerobic coverage for special sites (perirectal or genital → add cefepime 2 g IV every 8 hours plus metronidazole 500 mg IV every 8 hours, this formulary's gram-negative plus anaerobe pairing replacing piperacillin-tazobactam)

• Step-down and duration: switch IV to PO once drained, improving, afebrile, and tolerating oral intake → an MRSA-active oral agent as above; the duration is short — about 5–7 days when antibiotics are indicated (many simple drained abscesses need none); tailor to culture

• Recurrent abscesses → decolonization and workup: intranasal mupirocin twice daily for 5 days, chlorhexidine skin washes, and hygiene measures (laundering linens, avoiding sharing); treat household contacts if recurrent; evaluate for diabetes, immunodeficiency, HIV, and hidradenitis; involve ID

• PT/OT: rarely needed; wound care for packing and dressing changes

• Trend: the wound and drainage, surrounding erythema, fever and systemic signs, the response, culture and susceptibility (confirming an MRSA-active agent), and glucose if diabetic

• Escalation triggers: necrotizing features or systemic toxicity → emergent surgery; inadequate drainage or a persistent collection → repeat I&D or surgery with imaging; failure to improve → reassess the organism and coverage with ID; special-site or deep disease → a surgical specialty

• Discharge checklist: the abscess adequately drained and improving; an oral regimen (if indicated) with a short duration and stop date specified, MRSA-active; a wound-care and packing-change plan; recurrence prevention with a decolonization regimen, hygiene, and an underlying-cause workup if recurrent; culture follow-up; PCP, ID, or surgery follow-up; return precautions for spreading redness, increasing pain or swelling, fever, re-accumulation, or drainage changes

Red Flags

• Antibiotics instead of drainage → a walled-off abscess won't resolve without I&D

• Pain out of proportion or systemic toxicity → necrotizing infection → emergent surgery

• Special sites (perirectal, deep neck, hand, facial danger triangle) → involve the appropriate surgical specialty

• Recurrent abscesses → decolonize and evaluate for diabetes, immunodeficiency, or hidradenitis

• Inadequate drainage with a persistent collection → repeat I&D or surgical drainage

Senior IM Resident Pearls

• An abscess is plumbing, not pharmacology. The cure is opening it and letting it drain, and a simple drained abscess in a well patient often needs no antibiotics at all.

• Add MRSA-active antibiotics by criteria. Surrounding cellulitis, systemic signs, multiple or large abscesses, or an immunocompromised host are the triggers — and the drainage you send confirms the MRSA.

• For the patient who keeps coming back, decolonize. Mupirocin and chlorhexidine, plus a hunt for the reason (diabetes, hidradenitis, household MRSA), break the cycle of recurrence.

• Ultrasound settles the "is there pus?" question. A bedside scan distinguishes a drainable collection from cellulitis without fluid.

• The course is short. When antibiotics are indicated, about 5–7 days suffices — the drainage did the heavy lifting.

• Mind the special sites. Perirectal, deep neck, hand, and facial danger-triangle abscesses are not bedside I&D candidates — get the surgical specialty involved.

• Common mistake: prescribing antibiotics for a fluctuant abscess without draining it — the antibiotic can't penetrate the walled-off pus, and the patient returns unimproved.

Infectious Disease — Gynecologic

120. Pelvic Infection

pelvic inflammatory disease (PID) · tubo-ovarian abscess (TOA) · low threshold to treat (protect fertility) · ceftriaxone + doxycycline + metronidazole · drain large/refractory TOA · Super Compact

Sx: lower abdominal/pelvic pain (often bilateral), abnormal vaginal discharge, intermenstrual/postcoital bleeding, dyspareunia, fever; exam: cervical motion tenderness, uterine/adnexal tenderness (the minimum criteria) · TOA: adnexal mass, more systemic illness, higher fever · Fitz-Hugh-Curtis: perihepatitis → RUQ pain · (in a young woman with pelvic pain and cervical motion or adnexal tenderness, treat for PID empirically — the threshold is deliberately low because untreated PID costs fertility and risks ectopic pregnancy)

Neg: denies under-treating to protect fertility (low threshold — minimal criteria suffice) · denies missed TOA (needs imaging + possible drainage + inpatient IV) · denies missed ectopic pregnancy/appendicitis/ovarian torsion (surgical/obstetric emergencies) · denies missing partner treatment + other STI testing · denies missed pregnancy

SHx: sexual history (new/multiple partners, unprotected sex), prior STIs/PID (recurrence + tubal damage), recent IUD insertion (early), contraception, prior ectopic, douching; pregnancy status (changes management); HIV status

Etiology: ascending genital-tract infection (cervix → uterus → tubes → peritoneum) · sexually transmitted: Neisseria gonorrhoeae + Chlamydia trachomatis (key pathogens), plus polymicrobial — anaerobes (Bacteroides, Prevotella — drive the metronidazole need + TOA), gram-negatives, streptococci, Mycoplasma genitalium · TOA = walled-off abscess from progressive PID

RF: multiple/new sexual partners · prior STI/PID · age <25 · unprotected sex · recent IUD insertion · douching · prior tubal disease

Data: pregnancy test (always — rule out ectopic, guide therapy), NAAT for gonorrhea + chlamydia, HIV + syphilis + other STI screen · pelvic exam; pelvic/transvaginal ultrasound (TOA, mass, free fluid; rule out torsion/ectopic); CT if abscess/broad ddx · CBC, CMP, CRP, urinalysis, wet mount; blood cultures if systemically ill

DDx: PID · tubo-ovarian abscess · ectopic pregnancy (must exclude) · appendicitis · ovarian torsion/cyst · endometriosis · UTI/pyelonephritis · diverticulitis · ovarian/adnexal pathology

Home Meds: reconcile + renally dose abx; pregnancy-safe agent selection (avoid doxycycline in pregnancy — alternative regimen, OB-guided); analgesia; remove IUD only if no improvement (not automatically); resume after recovery

Plan

CONSULT: OB/Gynecology (TOA management, drainage, surgical evaluation, pregnancy, no response) · Interventional Radiology (image-guided TOA drainage) · Infectious Disease (complex/refractory, immunocompromised) · ICU (sepsis/ruptured TOA)

– TREAT EMPIRICALLY with a LOW THRESHOLD (minimal criteria: pelvic/lower-abdominal pain + cervical-motion OR uterine OR adnexal tenderness, no other cause) — protecting fertility outweighs over-treatment
– OUTPATIENT PID (mild–moderate, no TOA, tolerating PO, reliable): ceftriaxone 500 mg IM/IV single dose + doxycycline 100 mg PO BID × 14 days + metronidazole 500 mg PO BID × 14 days (the standard regimen — metronidazole adds anaerobic coverage)
– INPATIENT / SEVERE / TOA / pregnant / failed outpatient / unable to tolerate PO: IV — ceftriaxone 1 g IV q24h + doxycycline 100 mg IV/PO q12h + metronidazole 500 mg IV q8h; for severe/Pseudomonas-risk/healthcare-associated TOA, this formulary uses cefepime 2 g IV q8h + metronidazole 500 mg IV q8h + doxycycline (cefepime replaces piperacillin-tazobactam; metronidazole supplies the anaerobic cover cefepime lacks — important for abscess)
– TOA SOURCE CONTROL: drain large (>~7 cm) or non-responding TOA (image-guided IR or surgical); emergent surgery for ruptured TOA (peritonitis/sepsis) — antibiotics alone often fail for large abscesses
– STEP-DOWN + DURATION: IV→PO once afebrile ~24–48 h + clinically improving + abscess drained/responding + tolerating PO → oral doxycycline 100 mg BID + metronidazole 500 mg BID to complete 14 days total (TOA may need longer per response/imaging)
– STI care: treat presumptively for gonorrhea + chlamydia, test/treat sexual partners, counsel on STI prevention, retest as indicated; report per public health
– Treat PID on suspicion — the diagnostic bar is intentionally low because the cost of missing it is infertility, chronic pelvic pain, and ectopic pregnancy. The regimen always has three jobs: cover gonorrhea and chlamydia (ceftriaxone plus doxycycline) and cover anaerobes (metronidazole), which is non-negotiable when there's a tubo-ovarian abscess. Because this hospital stocks cefepime instead of Zosyn, a severe TOA needing broad gram-negative coverage becomes cefepime plus metronidazole plus doxycycline. And always do the pregnancy test first to rule out an ectopic, and treat the partner — otherwise she gets reinfected.
– PT/OT: rarely needed; post-op recovery if surgical
– Trend: pain, fever, adnexal exam/mass, WBC/CRP, ultrasound (TOA size/response), STI results, response to therapy
– Escalation triggers: no improvement in 48–72 h → imaging for TOA + drainage + gyn; ruptured TOA/peritonitis/sepsis → emergent surgery + ICU; large TOA → IR/surgical drainage; pregnancy → OB co-management
– Discharge checklist: improving + afebrile + (if TOA) drained/responding + tolerating oral regimen; oral doxycycline + metronidazole to complete 14 days (or longer for TOA) — total duration/stop date specified; partner treatment + STI counseling + HIV/syphilis results addressed; gyn follow-up (TOA imaging, fertility counseling); contraception/IUD plan; return precautions (worsening pain, fever, vomiting, fainting — ruptured TOA/ectopic, no improvement)

120. Pelvic Infection

complete reference · PID + tubo-ovarian abscess · low treatment threshold, ceftriaxone + doxycycline + metronidazole, drain large TOA, treat partners · Full Card

Symptoms / Associated Sx

• Lower abdominal or pelvic pain (often bilateral), abnormal vaginal discharge, intermenstrual or postcoital bleeding, dyspareunia, and fever

• Exam: cervical motion tenderness, and uterine or adnexal tenderness (the minimum criteria)

• TOA: an adnexal mass, more systemic illness, and a higher fever

• Fitz-Hugh-Curtis syndrome: perihepatitis causing RUQ pain

• In a young woman with pelvic pain and cervical motion or adnexal tenderness, treat for PID empirically — the threshold is deliberately low because untreated PID costs fertility and risks ectopic pregnancy

Neg

• Pt denies under-treating to protect fertility (a low threshold — minimal criteria suffice)

• Pt denies a missed TOA (needing imaging, possible drainage, and inpatient IV therapy) and a missed ectopic pregnancy, appendicitis, or ovarian torsion (surgical or obstetric emergencies)

• Pt denies missing partner treatment and other STI testing, and a missed pregnancy

Social History (SHx)

• Sexual history (new or multiple partners, unprotected sex), prior STIs or PID (recurrence and tubal damage), and recent IUD insertion (early)

• Contraception, prior ectopic pregnancy, and douching

• Pregnancy status (which changes management) and HIV status

Main Etiology

• An ascending genital-tract infection (cervix → uterus → tubes → peritoneum)

• Sexually transmitted: Neisseria gonorrhoeae and Chlamydia trachomatis (the key pathogens), plus polymicrobial organisms — anaerobes (Bacteroides, Prevotella — driving the metronidazole need and TOA), gram-negatives, streptococci, and Mycoplasma genitalium

• A TOA is a walled-off abscess from progressive PID

RF

• Modifiable: multiple or new sexual partners, unprotected sex, recent IUD insertion, and douching

• Non-modifiable: prior STI or PID, age under 25, and prior tubal disease

Data

• A pregnancy test (always — to rule out ectopic and guide therapy), NAAT for gonorrhea and chlamydia, and an HIV, syphilis, and other STI screen

• A pelvic exam; pelvic or transvaginal ultrasound (a TOA, mass, or free fluid; ruling out torsion and ectopic); and CT if there is an abscess or a broad differential

• CBC, CMP, CRP, urinalysis, and a wet mount; blood cultures if systemically ill

DDx

PID · a tubo-ovarian abscess · ectopic pregnancy (must exclude) · appendicitis · ovarian torsion or cyst · endometriosis · a UTI or pyelonephritis · diverticulitis · ovarian or adnexal pathology

Home Meds

• Reconcile and renally dose antibiotics; select pregnancy-safe agents (avoid doxycycline in pregnancy — an alternative regimen, OB-guided)

• Provide analgesia

• Remove the IUD only if there is no improvement (not automatically); resume medications after recovery

Plan

CONSULT: OB/Gynecology (TOA management, drainage, surgical evaluation, pregnancy, no response) · Interventional Radiology (image-guided TOA drainage) · Infectious Disease (complex or refractory disease, immunocompromise) · ICU (sepsis, a ruptured TOA)

• Treat empirically with a low threshold (minimal criteria: pelvic or lower-abdominal pain plus cervical-motion, uterine, or adnexal tenderness, with no other cause) — protecting fertility outweighs over-treatment

• Outpatient PID (mild–moderate, no TOA, tolerating oral intake, reliable): ceftriaxone 500 mg IM/IV as a single dose plus doxycycline 100 mg PO twice daily for 14 days plus metronidazole 500 mg PO twice daily for 14 days (the standard regimen — metronidazole adds anaerobic coverage)

• Inpatient / severe / TOA / pregnant / failed outpatient / unable to tolerate oral intake: IV — ceftriaxone 1 g IV every 24 hours plus doxycycline 100 mg IV/PO every 12 hours plus metronidazole 500 mg IV every 8 hours; for a severe, Pseudomonas-risk, or healthcare-associated TOA, this formulary uses cefepime 2 g IV every 8 hours plus metronidazole 500 mg IV every 8 hours plus doxycycline (cefepime replaces piperacillin-tazobactam, and metronidazole supplies the anaerobic coverage cefepime lacks — important for an abscess)

• TOA source control: drain a large (>~7 cm) or non-responding TOA (image-guided IR or surgical); emergent surgery for a ruptured TOA (peritonitis, sepsis) — antibiotics alone often fail for large abscesses

• Step-down and duration: switch IV to PO once the patient is afebrile for about 24–48 hours, clinically improving, with the abscess drained or responding, and tolerating oral intake → oral doxycycline 100 mg twice daily plus metronidazole 500 mg twice daily to complete 14 days total (a TOA may need longer per response and imaging)

• STI care: treat presumptively for gonorrhea and chlamydia, test and treat sexual partners, counsel on STI prevention, and retest as indicated; report per public health

• PT/OT: rarely needed; post-operative recovery if surgical

• Trend: pain, fever, the adnexal exam and mass, WBC/CRP, ultrasound (TOA size and response), STI results, and the response to therapy

• Escalation triggers: no improvement in 48–72 hours → imaging for a TOA, drainage, and gynecology; a ruptured TOA, peritonitis, or sepsis → emergent surgery and ICU; a large TOA → IR or surgical drainage; pregnancy → OB co-management

• Discharge checklist: improving, afebrile, with (if TOA) the abscess drained or responding, and tolerating the oral regimen; oral doxycycline and metronidazole to complete 14 days (or longer for a TOA) with the total duration and stop date specified; partner treatment, STI counseling, and HIV/syphilis results addressed; gynecology follow-up (TOA imaging, fertility counseling); a contraception or IUD plan; return precautions for worsening pain, fever, vomiting, or fainting (a ruptured TOA or ectopic, or no improvement)

Red Flags

• A ruptured TOA with peritonitis or sepsis → emergent surgery and ICU

• A missed ectopic pregnancy → always do the pregnancy test first

• A large or non-responding TOA → drainage; antibiotics alone often fail

• No improvement in 48–72 hours → image for a TOA and reassess the diagnosis

• Untreated partners → reinfection and ongoing tubal damage

Senior IM Resident Pearls

• Treat PID on suspicion. The diagnostic bar is intentionally low because the cost of missing it is infertility, chronic pelvic pain, and ectopic pregnancy.

• The regimen has three jobs. Cover gonorrhea and chlamydia (ceftriaxone plus doxycycline) and cover anaerobes (metronidazole) — the last is non-negotiable with a tubo-ovarian abscess.

• Cefepime plus metronidazole plus doxycycline for a severe TOA. Since the pharmacy stocks cefepime rather than Zosyn, that's how you build broad gram-negative plus anaerobic plus STI coverage.

• Pregnancy test first, every time. It rules out the ectopic that mimics PID and changes which antibiotics are safe.

• Treat the partner. Without partner treatment she gets reinfected, and the tubal damage compounds.

• Drain the big abscess. A TOA over about 7 cm or one that isn't responding needs image-guided or surgical drainage.

• Common mistake: reflexively pulling the IUD — leave it in initially and remove it only if there's no clinical improvement.

Infectious Disease — Bone/Joint

121. Prosthetic Joint Infection

infected hip/knee/shoulder arthroplasty · biofilm disease · ortho + ID joint management · surgical strategy (DAIR vs 1- or 2-stage exchange) + prolonged therapy + rifampin for staph · Super Compact

Sx: joint pain (the most consistent sign — esp persistent or new after arthroplasty), effusion, warmth, stiffness, reduced function; early/acute: wound drainage, dehiscence, erythema, fever, sinus tract; chronic/indolent: persistent pain ± loosening, often afebrile, subtle · (persistent or new pain in a prosthetic joint is PJI until proven otherwise — biofilm makes it indolent, so don't be reassured by the absence of fever or a normal-looking wound)

Neg: denies starting antibiotics before joint aspiration/operative cultures (need them to target a weeks-long course) · denies treating without a surgical plan (biofilm on hardware rarely clears with antibiotics alone) · denies missing a sinus tract (diagnostic of PJI) · denies missed acute hematogenous seeding (esp S. aureus bacteremia) · denies missed adjacent osteomyelitis

SHx: arthroplasty details (which joint, when implanted — early vs late, revision history), wound-healing problems/prior PJI, recent bacteremia (hematogenous seeding), diabetes/immunocompromise/RA, obesity, dental/other procedures, S. aureus colonization

Etiology: staphylococci dominate — coag-negative staph + S. aureus (biofilm formers); also streptococci, enterococci, gram-negatives (incl Pseudomonas), Cutibacterium (shoulder), polymicrobial · biofilm on the implant shields bacteria from antibiotics + immunity → indolent, relapsing, hardware-dependent · timing: early post-op (≤3 mo), delayed (3–12 mo, low-virulence), late hematogenous (>12 mo, seeded)

RF: prior PJI/revision · wound-healing complications · S. aureus colonization · diabetes/immunocompromise/RA · obesity · recent bacteremia · prolonged surgery

Data: JOINT ASPIRATION — synovial fluid: cell count (elevated WBC %PMN, lower thresholds than native joint), culture, crystals; HOLD antibiotics until cultured if stable · ≥3–5 intraoperative tissue cultures + sonication of explanted hardware (improves yield) · ESR + CRP (elevated; useful screen/trend), CBC, blood cultures (esp acute/hematogenous) · X-ray (loosening/lucency), MRI/nuclear if needed · synovial alpha-defensin (adjunct)

DDx: prosthetic joint infection · aseptic loosening (mechanical, non-infectious) · native/adjacent osteomyelitis · crystal arthropathy · hematoma · periprosthetic fracture · referred pain · inflammatory arthritis flare

Home Meds: hold immunosuppressants/biologics per rheum during infection · reconcile + renally dose abx · plan long-term IV access (PICC) + prolonged oral phase · DDIs with rifampin (potent CYP inducer — warfarin, many drugs) · anticoagulation for surgery

Plan

CONSULT: Orthopedic Surgery (the surgical strategy — DAIR vs exchange — is central) · Infectious Disease (organism-directed prolonged therapy, rifombin/biofilm regimens, duration — essential, co-management) · Plastics (soft-tissue coverage if needed) · Antimicrobial Stewardship

– SURGICAL STRATEGY (ortho-led, decided WITH ID — antibiotics rarely cure biofilm alone):
  • DAIR (debridement, antibiotics, implant retention): for EARLY post-op or acute hematogenous infection with a stable, well-fixed implant, short symptom duration, and a susceptible organism — debride, exchange modular parts, retain the prosthesis
  • Two-stage exchange (the gold standard for chronic PJI): remove the prosthesis, place an antibiotic spacer, treat, then reimplant — best cure rate for chronic/loose/resistant infection
  • One-stage exchange: selected cases (known susceptible organism, good soft tissue)
  • Suppression: chronic oral suppression when surgery isn't feasible (poor candidate) — controls, doesn't cure
– EMPIRIC ANTIBIOTICS (AFTER cultures/surgery; broad then narrow; THIS FORMULARY uses cefepime, not piperacillin-tazobactam): vancomycin IV (MRSA/coag-neg staph) + cefepime 2 g IV q8h (gram-negative incl Pseudomonas)
– TARGETED therapy (by operative cultures — narrow): MSSA → cefazolin 2 g IV q8h (or nafcillin); MRSA → vancomycin; streptococci → ceftriaxone/penicillin; gram-negative → per susceptibility
  • STAPHYLOCOCCAL PJI with RETAINED hardware (DAIR or 1-stage) → ADD RIFAMPIN (biofilm penetration — the key biofilm-active agent) combined with a companion agent (e.g. rifampin + a fluoroquinolone for staph) — never rifampin monotherapy (rapid resistance); start rifampin once wound is dry/drains out per ID
– DURATION + STEP-DOWN: typically weeks of initial IV then transition to oral to complete a prolonged course — commonly ~6 weeks of effective therapy after DAIR/1-stage (often IV→highly bioavailable oral, e.g. fluoroquinolone + rifampin for staph); 2-stage: ~6 weeks between stages then reassess before reimplant; IV→PO once clinically stable, wound healing, inflammatory markers improving, on a susceptible bioavailable oral regimen (OVIVA supports oral for bone/joint infection in selected patients)
– Supportive: analgesia, glucose control, nutrition optimization, VTE prophylaxis, manage DDIs (rifampin), monitor for relapse
– PJI is a biofilm disease, which means the surgeon decides the outcome as much as the antibiotic: bacteria living on the implant are shielded from drugs and immunity, so a plan that doesn't address the hardware usually fails. Early, stable infections with a good organism can keep the implant via DAIR; chronic ones almost always need a two-stage exchange. The one antibiotic detail that's specific to retained hardware is rifampin — it penetrates staphylococcal biofilm and dramatically improves cure, but it must always ride with a companion agent because alone it breeds resistance fast. And as everywhere in this handbook, when you need broad gram-negative coverage it's cefepime, not Zosyn.
– PT/OT: central — mobility, weight-bearing per ortho, rehab through staged procedures, function preservation
– Trend: joint pain/function, wound healing/drainage, ESR/CRP (downtrend), cultures/susceptibility, rifampin DDIs/tolerance, reimplant readiness (2-stage)
– Escalation triggers: failure/relapse on DAIR → escalate to exchange + ID; persistent drainage/wound breakdown → re-debridement ± plastics; sepsis/acute hematogenous with bacteremia → source + blood-culture clearance + ID; resistant organism → ID regimen revision
– Discharge checklist: surgical strategy defined + executed/planned + organism-directed regimen set; OPAT/PICC then validated oral phase (incl rifampin + companion for staph) with total duration/stop date + reimplant plan (2-stage) specified; ID + ortho follow-up + inflammatory-marker monitoring; PT plan; rifampin DDI counseling (warfarin/other); dental + future-procedure prophylaxis counseling; return precautions (increasing joint pain, wound drainage/breakdown, fever, function loss)

121. Prosthetic Joint Infection

complete reference · biofilm disease · ortho + ID co-management, surgical strategy (DAIR vs exchange), rifampin for retained staph hardware, prolonged therapy · Full Card

Symptoms / Associated Sx

• Joint pain (the most consistent sign, especially persistent or new pain after arthroplasty), an effusion, warmth, stiffness, and reduced function

• Early or acute disease: wound drainage, dehiscence, erythema, fever, and a sinus tract

• Chronic or indolent disease: persistent pain with possible loosening, often afebrile and subtle

• Persistent or new pain in a prosthetic joint is PJI until proven otherwise — biofilm makes it indolent, so don't be reassured by the absence of fever or a normal-looking wound

Neg

• Pt denies starting antibiotics before joint aspiration or operative cultures (they're needed to target a weeks-long course)

• Pt denies treating without a surgical plan (biofilm on hardware rarely clears with antibiotics alone) and missing a sinus tract (diagnostic of PJI)

• Pt denies a missed acute hematogenous seeding (especially S. aureus bacteremia) and a missed adjacent osteomyelitis

Social History (SHx)

• Arthroplasty details (which joint, when implanted — early versus late, revision history), wound-healing problems, and prior PJI

• Recent bacteremia (hematogenous seeding), diabetes, immunocompromise, or RA

• Obesity, dental or other procedures, and S. aureus colonization

Main Etiology

• Staphylococci dominate — coagulase-negative staph and S. aureus (biofilm formers); also streptococci, enterococci, gram-negatives (including Pseudomonas), Cutibacterium (shoulder), and polymicrobial infection

• Biofilm on the implant shields bacteria from antibiotics and immunity, producing an indolent, relapsing, hardware-dependent infection

• Timing: early post-operative (≤3 months), delayed (3–12 months, low-virulence), and late hematogenous (>12 months, seeded)

RF

• Modifiable: wound-healing complications, S. aureus colonization, glycemic control, and obesity

• Non-modifiable: prior PJI or revision, immunocompromise or RA, recent bacteremia, and prolonged surgery

Data

• Joint aspiration — synovial fluid for a cell count (an elevated WBC and %PMN, with lower thresholds than a native joint), culture, and crystals; hold antibiotics until cultured if the patient is stable

• Three to five intraoperative tissue cultures plus sonication of explanted hardware (improving yield)

• ESR and CRP (elevated; a useful screen and trend), CBC, and blood cultures (especially acute or hematogenous disease)

• X-ray (loosening, lucency), MRI or nuclear imaging if needed, and synovial alpha-defensin (an adjunct)

DDx

Prosthetic joint infection · aseptic loosening (mechanical, non-infectious) · native or adjacent osteomyelitis · crystal arthropathy · a hematoma · a periprosthetic fracture · referred pain · an inflammatory arthritis flare

Home Meds

• Hold immunosuppressants and biologics per rheumatology during infection

• Reconcile and renally dose antibiotics; plan long-term IV access (a PICC) and a prolonged oral phase

• Manage drug interactions with rifampin (a potent CYP inducer — warfarin and many drugs) and anticoagulation for surgery

Plan

CONSULT: Orthopedic Surgery (the surgical strategy — DAIR versus exchange — is central) · Infectious Disease (organism-directed prolonged therapy, rifampin/biofilm regimens, duration — essential, co-management) · Plastics (soft-tissue coverage if needed) · Antimicrobial Stewardship

• Surgical strategy (ortho-led, decided with ID — antibiotics rarely cure biofilm alone):

• • DAIR (debridement, antibiotics, implant retention): for early post-operative or acute hematogenous infection with a stable, well-fixed implant, short symptom duration, and a susceptible organism — debride, exchange modular parts, and retain the prosthesis

• • Two-stage exchange (the gold standard for chronic PJI): remove the prosthesis, place an antibiotic spacer, treat, then reimplant — the best cure rate for chronic, loose, or resistant infection

• • One-stage exchange: selected cases (a known susceptible organism, good soft tissue)

• • Suppression: chronic oral suppression when surgery isn't feasible (a poor candidate) — controls but doesn't cure

• Empiric antibiotics (after cultures and surgery; broad then narrow; this formulary uses cefepime, not piperacillin-tazobactam): vancomycin IV (MRSA, coagulase-negative staph) plus cefepime 2 g IV every 8 hours (gram-negatives including Pseudomonas)

• Targeted therapy (by operative cultures — narrow): MSSA → cefazolin 2 g IV every 8 hours (or nafcillin); MRSA → vancomycin; streptococci → ceftriaxone or penicillin; gram-negatives → per susceptibility

• • Staphylococcal PJI with retained hardware (DAIR or 1-stage) → add rifampin (biofilm penetration — the key biofilm-active agent) combined with a companion agent (e.g. rifampin plus a fluoroquinolone for staph) — never rifampin monotherapy (rapid resistance); start rifampin once the wound is dry or drains are out per ID

• Duration and step-down: typically weeks of initial IV then transition to oral to complete a prolonged course — commonly about 6 weeks of effective therapy after DAIR or 1-stage exchange (often IV then a highly bioavailable oral, e.g. a fluoroquinolone plus rifampin for staph); 2-stage exchange: about 6 weeks between stages then reassessment before reimplant; switch IV to PO once clinically stable, the wound is healing, inflammatory markers are improving, and on a susceptible bioavailable oral regimen (OVIVA supports oral therapy for bone and joint infection in selected patients)

• Supportive care: analgesia, glucose control, nutrition optimization, VTE prophylaxis, management of drug interactions (rifampin), and monitoring for relapse

• PT/OT: central — mobility, weight-bearing per ortho, rehabilitation through staged procedures, and function preservation

• Trend: joint pain and function, wound healing and drainage, ESR/CRP (a downtrend), cultures and susceptibility, rifampin interactions and tolerance, and reimplant readiness (2-stage)

• Escalation triggers: failure or relapse on DAIR → escalate to exchange with ID; persistent drainage or wound breakdown → re-debridement with plastics; sepsis or acute hematogenous disease with bacteremia → source control, blood-culture clearance, and ID; a resistant organism → an ID regimen revision

• Discharge checklist: the surgical strategy defined and executed or planned with an organism-directed regimen set; OPAT/PICC then a validated oral phase (including rifampin plus a companion for staph) with the total duration and stop date, and a reimplant plan (2-stage) specified; ID and ortho follow-up with inflammatory-marker monitoring; a PT plan; rifampin interaction counseling (warfarin and others); dental and future-procedure prophylaxis counseling; return precautions for increasing joint pain, wound drainage or breakdown, fever, or function loss

Red Flags

• Treating biofilm with antibiotics alone → rarely curative; the surgical strategy is central

• A sinus tract communicating with the prosthesis → diagnostic of PJI

• Rifampin monotherapy → rapid resistance; it must always have a companion agent

• Acute hematogenous PJI with S. aureus bacteremia → an endovascular source workup and blood-culture clearance

• Failure or relapse on DAIR → escalate to a staged exchange

Senior IM Resident Pearls

• PJI is a biofilm disease — the surgeon decides the outcome. Bacteria on the implant are shielded from drugs and immunity, so a plan that doesn't address the hardware usually fails.

• DAIR for early and stable, exchange for chronic. Short-duration infections with a good organism and a well-fixed implant can keep it; chronic ones almost always need a two-stage exchange.

• Rifampin is the biofilm agent for retained staph hardware — but never alone. It penetrates biofilm and improves cure, yet it breeds resistance fast without a companion agent.

• Get the cultures before antibiotics. Hold therapy in a stable patient until joint aspiration or operative cultures define the organism that guides weeks of treatment.

• Don't be reassured by a normal temperature. Indolent PJI is often afebrile with a benign-looking wound — persistent pain is the red flag.

• Mind the rifampin interactions. It's a potent CYP inducer that decimates warfarin and many other drugs — reconcile carefully before starting.

• Common mistake: treating "aseptic loosening" pain as purely mechanical without aspirating — a missed low-grade PJI relapses after revision and wastes the surgery.

Infectious Disease — CNS/Spine

122. Spinal Epidural Abscess

back pain + fever + neurologic symptoms · NEUROSURGICAL EMERGENCY · urgent whole-spine MRI + emergent decompression before irreversible deficit · vancomycin + cefepime · Super Compact

Sx: classic triad: back pain (focal, severe) + fever + neurologic deficit (the full triad is often INCOMPLETE/late) · progression: back pain → radicular pain → motor/sensory deficits, bowel/bladder dysfunction → paralysis; point tenderness over the spine · (back pain + fever — especially with any neurologic symptom or an IVDU/bacteremic patient — is a spinal epidural abscess until an MRI says otherwise; the window to preserve neurologic function is short, so this is a "scan now" diagnosis)

Neg: denies delaying MRI/decompression when suspected (neuro deficits can become permanent within hours — emergency) · denies starting antibiotics before cultures if stable + no rapidly progressing deficit (blood cultures/biopsy guide therapy) — BUT denies delaying abx in a septic/rapidly deteriorating patient · denies missed concurrent vertebral osteomyelitis/discitis · denies missed endocarditis/other seeding source

SHx: IVDU (major risk), recent bacteremia/S. aureus infection, diabetes/immunocompromise, recent spinal procedure/epidural/surgery, indwelling catheters/hemodialysis, chronic back disease, skin/soft-tissue infection (seeding source)

Etiology: S. aureus is the most common (incl MRSA); also gram-negatives, streptococci, coag-neg staph (post-procedural) · spread hematogenous (most — from skin, endocarditis, IVDU), contiguous (vertebral osteomyelitis/discitis, psoas abscess), or direct inoculation (procedures) · pus in the epidural space → cord/root compression + ischemia → neurologic injury

RF: IVDU · recent bacteremia/S. aureus infection · diabetes/immunocompromise · spinal procedure/surgery/epidural · indwelling devices/hemodialysis · chronic back disease

Data: URGENT MRI of the WHOLE spine with contrast (the diagnostic test — skip levels common; defines extent/compression) · blood cultures (frequently positive) + culture from CT-guided/operative aspiration (organism for targeted therapy) · ESR + CRP (markedly elevated), CBC, CMP · echocardiogram (concurrent endocarditis — esp S. aureus/IVDU); HIV; spine X-ray/CT adjunct

DDx: spinal epidural abscess · vertebral osteomyelitis/discitis (often coexist) · cord compression (tumor/metastasis/hematoma) · transverse myelitis · mechanical back pain · meningitis · cauda equina syndrome (other causes) · psoas abscess

Home Meds: hold anticoagulants/antiplatelets if surgery/biopsy planned (bleeding); reconcile + renally dose abx; plan long-term IV access; address IVDU/addiction; stress-dose steroids if chronic

Plan

CONSULT: Neurosurgery (URGENT/EMERGENT — surgical decompression + drainage; the priority) · Infectious Disease (organism-directed prolonged therapy + duration) · Interventional Radiology (CT-guided aspiration if no operative indication) · Cardiology (concurrent endocarditis) · Addiction Medicine (IVDU)

– EMERGENT NEUROSURGICAL DECOMPRESSION + DRAINAGE is the definitive treatment for cord/root compression or neurologic deficit (laminectomy/drainage) — time-critical: deficits can become irreversible within hours, so don't wait; selected small abscesses without deficit may be managed with antibiotics + close monitoring (neurosurgery decision)
– GET CULTURES THEN TREAT: blood cultures + image-guided/operative aspiration for organism; in a stable patient without rapidly progressing deficit, obtaining cultures before antibiotics helps targeting — but do NOT delay antibiotics in a septic or rapidly deteriorating patient
– EMPIRIC ANTIBIOTICS (cover S. aureus incl MRSA + gram-negatives; THIS FORMULARY uses cefepime, not piperacillin-tazobactam): vancomycin IV (MRSA) + cefepime 2 g IV q8h (gram-negative incl Pseudomonas)
– TARGETED therapy (by culture — narrow): MSSA → cefazolin 2 g IV q8h (or nafcillin); MRSA → vancomycin; gram-negative → per susceptibility; streptococci → ceftriaxone/penicillin
– DURATION + STEP-DOWN: prolonged — typically ~6 weeks of targeted therapy (longer with concurrent vertebral osteomyelitis); generally IV initially, with step-down to a highly bioavailable oral agent (per OVIVA, in selected stable patients with good source control + susceptible organism) to complete the course (ID-directed) — e.g. oral fluoroquinolone ± rifampin for susceptible staph; IV→PO once neurologically stable, source controlled, inflammatory markers improving, on a susceptible bioavailable oral regimen
– EVALUATE the seeding source: echo (endocarditis), search for primary focus; treat concurrent vertebral osteomyelitis/discitis (often present) on the same prolonged plan
– Supportive: serial neuro exams (detect deterioration early), analgesia, glucose control, VTE prophylaxis, bladder management, addiction treatment (IVDU)
– This is a "scan now, call neurosurgery now" diagnosis. Back pain plus fever — especially in an IVDU or bacteremic patient, and doubly so with any neurologic symptom — demands an urgent MRI of the entire spine, because skip lesions are common and the window to save cord function is measured in hours, not days. S. aureus drives most cases, so empiric coverage is vancomycin plus cefepime (the local stand-in for Zosyn). The thing that hurts patients is delay: a deficit that's present at decompression often improves, but one allowed to progress to paralysis frequently doesn't recover. Hunt for the source too — many of these patients have endocarditis seeding the spine.
– PT/OT: central — neuro rehab, mobility, function recovery; bladder/bowel management
– Trend: serial neuro exams (motor/sensory/bladder), back pain, fever, ESR/CRP (downtrend), cultures, repeat MRI if deteriorating, echo results
– Escalation triggers: any new/progressing neuro deficit → emergent neurosurgery/repeat decompression; sepsis → ICU + sepsis pathway; persistent bacteremia → endovascular source (endocarditis) workup + ID; failure to improve → reimage (residual/expanding abscess)
– Discharge checklist: decompressed/source-controlled + neurologically stable/improving + organism-directed regimen; OPAT/PICC then validated oral phase, total duration (~6 wk+)/stop date specified; ID + neurosurgery follow-up + inflammatory-marker monitoring; repeat imaging plan; PT/rehab + bladder plan; endocarditis evaluation completed; addiction treatment linkage (IVDU); return precautions (new/worsening weakness/numbness, bowel/bladder changes, worsening back pain, fever)

122. Spinal Epidural Abscess

complete reference · back pain + fever + neuro symptoms · emergent whole-spine MRI + neurosurgical decompression, vancomycin + cefepime, ~6 weeks · Full Card

Symptoms / Associated Sx

• The classic triad: focal, severe back pain, fever, and a neurologic deficit (the full triad is often incomplete or late)

• Progression: back pain → radicular pain → motor and sensory deficits and bowel/bladder dysfunction → paralysis; point tenderness over the spine

• Back pain with fever — especially with any neurologic symptom or in an IVDU or bacteremic patient — is a spinal epidural abscess until an MRI says otherwise; the window to preserve neurologic function is short, so this is a "scan now" diagnosis

Neg

• Pt denies delaying MRI or decompression when suspected (neurologic deficits can become permanent within hours — an emergency)

• Pt denies starting antibiotics before cultures if stable and without a rapidly progressing deficit (blood cultures and biopsy guide therapy) — but denies delaying antibiotics in a septic or rapidly deteriorating patient

• Pt denies a missed concurrent vertebral osteomyelitis or discitis and a missed endocarditis or other seeding source

Social History (SHx)

• IV drug use (a major risk), recent bacteremia or S. aureus infection, and diabetes or immunocompromise

• A recent spinal procedure, epidural, or surgery, and indwelling catheters or hemodialysis

• Chronic back disease and skin or soft-tissue infection (a seeding source)

Main Etiology

• S. aureus is the most common cause (including MRSA); also gram-negatives, streptococci, and coagulase-negative staph (post-procedural)

• Spread is hematogenous (most — from skin, endocarditis, IVDU), contiguous (vertebral osteomyelitis, discitis, psoas abscess), or by direct inoculation (procedures)

• Pus in the epidural space causes cord and root compression and ischemia, producing neurologic injury

RF

• Modifiable: IV drug use, a recent spinal procedure or surgery, and indwelling devices

• Non-modifiable: recent bacteremia or S. aureus infection, diabetes or immunocompromise, hemodialysis, and chronic back disease

Data

• Urgent MRI of the whole spine with contrast (the diagnostic test — skip levels are common; it defines the extent and compression)

• Blood cultures (frequently positive) plus culture from CT-guided or operative aspiration (the organism for targeted therapy)

• ESR and CRP (markedly elevated), CBC, and CMP

• An echocardiogram (concurrent endocarditis — especially with S. aureus or IVDU); HIV testing; and spine X-ray or CT as an adjunct

DDx

Spinal epidural abscess · vertebral osteomyelitis or discitis (often coexist) · cord compression (tumor, metastasis, hematoma) · transverse myelitis · mechanical back pain · meningitis · cauda equina syndrome (other causes) · a psoas abscess

Home Meds

• Hold anticoagulants and antiplatelets if surgery or biopsy is planned (bleeding)

• Reconcile and renally dose antibiotics; plan long-term IV access

• Address IVDU and addiction; stress-dose steroids if there is chronic use

Plan

CONSULT: Neurosurgery (urgent/emergent — surgical decompression and drainage; the priority) · Infectious Disease (organism-directed prolonged therapy and duration) · Interventional Radiology (CT-guided aspiration if there is no operative indication) · Cardiology (concurrent endocarditis) · Addiction Medicine (IVDU)

• Emergent neurosurgical decompression and drainage is the definitive treatment for cord or root compression or a neurologic deficit (laminectomy and drainage) — time-critical: deficits can become irreversible within hours, so don't wait; selected small abscesses without a deficit may be managed with antibiotics and close monitoring (a neurosurgery decision)

• Get cultures then treat: blood cultures plus image-guided or operative aspiration for the organism; in a stable patient without a rapidly progressing deficit, obtaining cultures before antibiotics helps targeting — but do not delay antibiotics in a septic or rapidly deteriorating patient

• Empiric antibiotics (covering S. aureus including MRSA and gram-negatives; this formulary uses cefepime, not piperacillin-tazobactam): vancomycin IV (MRSA) plus cefepime 2 g IV every 8 hours (gram-negatives including Pseudomonas)

• Targeted therapy (by culture — narrow): MSSA → cefazolin 2 g IV every 8 hours (or nafcillin); MRSA → vancomycin; gram-negatives → per susceptibility; streptococci → ceftriaxone or penicillin

• Duration and step-down: prolonged — typically about 6 weeks of targeted therapy (longer with concurrent vertebral osteomyelitis); generally IV initially, with step-down to a highly bioavailable oral agent (per OVIVA, in selected stable patients with good source control and a susceptible organism) to complete the course (ID-directed) — e.g. an oral fluoroquinolone with or without rifampin for susceptible staph; switch IV to PO once neurologically stable, the source is controlled, inflammatory markers are improving, and on a susceptible bioavailable oral regimen

• Evaluate the seeding source: an echo (endocarditis) and a search for the primary focus; treat concurrent vertebral osteomyelitis or discitis (often present) on the same prolonged plan

• Supportive care: serial neuro exams (to detect deterioration early), analgesia, glucose control, VTE prophylaxis, bladder management, and addiction treatment (IVDU)

• PT/OT: central — neuro rehabilitation, mobility, function recovery, and bladder/bowel management

• Trend: serial neuro exams (motor, sensory, bladder), back pain, fever, ESR/CRP (a downtrend), cultures, a repeat MRI if deteriorating, and echo results

• Escalation triggers: any new or progressing neurologic deficit → emergent neurosurgery and repeat decompression; sepsis → ICU and the sepsis pathway; persistent bacteremia → an endovascular source (endocarditis) workup and ID; failure to improve → reimage (a residual or expanding abscess)

• Discharge checklist: decompressed and source-controlled, neurologically stable or improving, on an organism-directed regimen; OPAT/PICC then a validated oral phase, with the total duration (~6 weeks or more) and stop date specified; ID and neurosurgery follow-up with inflammatory-marker monitoring; a repeat imaging plan; PT/rehabilitation and a bladder plan; the endocarditis evaluation completed; addiction treatment linkage (IVDU); return precautions for new or worsening weakness or numbness, bowel or bladder changes, worsening back pain, or fever

Red Flags

• Any new or progressing neurologic deficit → emergent decompression; the window is hours, not days

• Back pain plus fever in an IVDU or bacteremic patient → MRI the whole spine urgently (skip lesions are common)

• Bowel or bladder dysfunction → impending or established cord compression

• Persistent S. aureus bacteremia → an endovascular source; obtain an echocardiogram

• Failure to improve → a residual or expanding abscess; reimage and reconsider decompression

Senior IM Resident Pearls

• This is a "scan now, call neurosurgery now" diagnosis. Back pain plus fever — especially with any neurologic symptom — demands an urgent MRI of the entire spine.

• Image the whole spine. Skip lesions at non-contiguous levels are common, so a single-level scan can miss disease.

• Delay is what causes paralysis. A deficit present at decompression often improves, but one allowed to progress to paralysis frequently doesn't recover.

• Cover S. aureus empirically. Vancomycin plus cefepime is the local empiric pair, since cefepime stands in for Zosyn here.

• Hunt for the source. Many patients have endocarditis seeding the spine — get an echo, especially in S. aureus bacteremia or IVDU.

• Vertebral osteomyelitis usually travels with it. Treat the concurrent bone infection on the same prolonged plan.

• Common mistake: attributing severe back pain to "mechanical" causes in a febrile or bacteremic patient and skipping the MRI — that delay is exactly what costs neurologic function.

Infectious Disease — Skin/Soft Tissue

123. Necrotizing Soft Tissue Infection

necrotizing fasciitis / "flesh-eating" infection · SURGICAL EMERGENCY · emergent debridement is life-saving — don't delay for imaging · broad abx + clindamycin (toxin) · Super Compact

Sx: PAIN OUT OF PROPORTION to exam (the cardinal early clue), rapidly spreading erythema/edema, systemic toxicity (fever, tachycardia, hypotension, AMS) · late/ominous: skin necrosis/dusky discoloration, hemorrhagic bullae, crepitus (gas), skin anesthesia (nerve destruction), "dishwater" drainage, woody-hard induration extending beyond visible erythema · (pain out of proportion + a toxic-appearing patient is necrotizing infection until surgery proves otherwise — the disease moves by the hour, so suspicion alone justifies an emergent surgical consult)

Neg: denies delaying surgical exploration/debridement for imaging or labs (surgery is both diagnostic + life-saving — every hour of delay raises mortality) · denies treating as simple cellulitis (under-recognition kills) · denies missed gas gangrene/Fournier (perineal) · denies inadequate broad + toxin-suppressing coverage · denies missed source/septic shock

SHx: diabetes (major risk), immunocompromise, IVDU, peripheral vascular disease, recent trauma/surgery/skin breach, cirrhosis/chronic liver disease (Vibrio — seawater/raw shellfish), obesity, age; perineal source (Fournier — diabetics/males)

Etiology: Type I (polymicrobial): mixed aerobes + anaerobes (diabetics, post-op, perineal/Fournier) · Type II (monomicrobial): Group A Streptococcus (± toxic shock), also S. aureus (incl MRSA) · Type III: Vibrio/Aeromonas (water exposure, cirrhosis), Clostridium (gas gangrene) · rapid fascial-plane spread + thrombosis of perforating vessels → ischemic necrosis outpacing the visible skin

RF: diabetes · immunocompromise · IVDU · PVD · recent trauma/surgery · cirrhosis (Vibrio) · obesity · perineal infection (Fournier)

Data: this is a CLINICAL/SURGICAL diagnosis — do NOT delay surgery for tests · supportive: CBC, CMP, lactate, CRP, CK (muscle), coags, blood cultures; LRINEC score (adjunct, not a rule-out) · imaging (CT/MRI — fascial gas/edema) ONLY if it won't delay surgery in a stable patient; operative findings + Gram stain/culture of tissue confirm + guide

DDx: necrotizing soft tissue infection · severe cellulitis/erysipelas · abscess · gas gangrene (clostridial myonecrosis) · pyomyositis · DVT · compartment syndrome · Fournier gangrene (perineal subtype)

Home Meds: NPO (emergent surgery); hold anticoagulants/oral agents pre-op; reconcile + renally dose abx; aggressive resuscitation; stress-dose steroids if chronic; hold metformin (AKI/lactic acidosis)

Plan

CONSULT: Surgery (EMERGENT — immediate operative exploration + aggressive debridement; THE priority, repeated as needed) · ICU (septic shock, resuscitation) · Infectious Disease (antibiotic tailoring, toxin management) · Urology/Gyn (Fournier) · Plastics (reconstruction after) · Hyperbaric (adjunct, select centers)

– EMERGENT SURGICAL DEBRIDEMENT is the definitive, life-saving treatment — do NOT delay for imaging/labs: immediate operative exploration; aggressive excision of all necrotic tissue; plan repeat "second-look" debridements q24h until no further necrosis; amputation if limb non-salvageable; antibiotics + ICU support are adjuncts to surgery, never substitutes
– BROAD EMPIRIC ANTIBIOTICS immediately (cover gram-pos incl MRSA + gram-neg incl Pseudomonas + anaerobes + toxin; THIS FORMULARY uses cefepime, not piperacillin-tazobactam):
  • Vancomycin IV (MRSA) + cefepime 2 g IV q8h (gram-negative incl Pseudomonas) + metronidazole 500 mg IV q8h (anaerobes — cefepime lacks anaerobic cover, so add it; together replaces the broad single-agent role of Zosyn) + clindamycin 900 mg IV q8h
  • CLINDAMYCIN is added specifically to SUPPRESS TOXIN production (Streptococcus/Staphylococcus exotoxins — the "Eagle effect"; protein-synthesis inhibition reduces toxin even at high bacterial loads) — keep on until clinically stable/source controlled
– AGGRESSIVE RESUSCITATION + ICU: fluids, vasopressors, organ support (sepsis/septic shock pathway); these patients are critically ill
– TARGET once cultures/operative data return (narrow): Group A Strep → penicillin + clindamycin; MRSA → continue vancomycin; Vibrio (water/cirrhosis) → doxycycline + ceftriaxone/cefepime; Clostridium → penicillin + clindamycin
– IVIG may be considered for streptococcal toxic shock / severe Group A Strep (adjunct, per ID/critical care)
– DURATION + STEP-DOWN: continue IV until source controlled (no further necrosis on serial debridement), hemodynamically stable, afebrile, improving — duration is individualized (commonly continued for a period after the last debridement); step down to a culture-directed oral agent once source is definitively controlled, off pressors, afebrile, tolerating PO + an active oral option; clindamycin can stop once stable/toxin risk resolved
– The single message of this card: when you suspect necrotizing infection, the patient goes to the OR — surgery is both how you confirm it and how you save the patient, and every hour of delay for a CT or a LRINEC score raises mortality. Pain out of proportion to an unimpressive-looking exam in a toxic patient is the early tell, long before the dramatic skin findings appear. Antibiotics are essential but adjunctive: broad coverage (here vancomycin + cefepime + metronidazole, since cefepime needs the metronidazole for anaerobes) plus clindamycin, which earns its place by shutting down the streptococcal and staphylococcal toxins that drive the shock. Then resuscitate hard and plan to go back to the OR daily until the necrosis stops.
– PT/OT: later — extensive rehab, wound care, reconstruction, functional recovery after debridements
– Trend: wound/debridement margins (serial), hemodynamics/pressor needs, lactate, organ function, WBC/CK, cultures, response; daily surgical reassessment
– Escalation triggers: ongoing necrosis → return to OR (repeat debridement); refractory shock → ICU escalation; new compartment involvement → fasciotomy/amputation decision; streptococcal TSS → IVIG; failure → ID + broaden/reassess
– Discharge checklist: source definitively controlled (no further necrosis) + hemodynamically stable + wounds managed; oral/IV regimen with total duration/stop date specified, culture-directed; extensive wound-care + reconstruction plan; surgery + ID + plastics + rehab follow-up; nutrition optimization; diabetes/underlying-condition management; return precautions (recurrent fever, wound deterioration/new necrosis, spreading pain/redness, systemic illness)

123. Necrotizing Soft Tissue Infection

complete reference · surgical emergency · emergent debridement (don't delay for imaging) + broad abx + clindamycin for toxin + ICU resuscitation · Full Card

Symptoms / Associated Sx

• Pain out of proportion to the exam (the cardinal early clue), rapidly spreading erythema and edema, and systemic toxicity (fever, tachycardia, hypotension, altered mental status)

• Late, ominous signs: skin necrosis or dusky discoloration, hemorrhagic bullae, crepitus (gas), skin anesthesia (nerve destruction), "dishwater" drainage, and woody-hard induration extending beyond the visible erythema

• Pain out of proportion in a toxic-appearing patient is necrotizing infection until surgery proves otherwise — the disease moves by the hour, so suspicion alone justifies an emergent surgical consult

Neg

• Pt denies delaying surgical exploration or debridement for imaging or labs (surgery is both diagnostic and life-saving — every hour of delay raises mortality)

• Pt denies treating it as simple cellulitis (under-recognition kills) and a missed gas gangrene or Fournier (perineal) disease

• Pt denies inadequate broad and toxin-suppressing coverage and a missed source or septic shock

Social History (SHx)

• Diabetes (a major risk), immunocompromise, IV drug use, and peripheral vascular disease

• Recent trauma, surgery, or a skin breach, and cirrhosis or chronic liver disease (Vibrio — from seawater or raw shellfish)

• Obesity, age, and a perineal source (Fournier — in diabetics and males)

Main Etiology

• Type I (polymicrobial): mixed aerobes and anaerobes (diabetics, post-operative, perineal/Fournier)

• Type II (monomicrobial): Group A Streptococcus (with possible toxic shock), and also S. aureus (including MRSA)

• Type III: Vibrio or Aeromonas (water exposure, cirrhosis) and Clostridium (gas gangrene)

• Rapid fascial-plane spread and thrombosis of perforating vessels cause ischemic necrosis that outpaces the visible skin

RF

• Modifiable: IV drug use, recent trauma or surgery, and obesity

• Non-modifiable: diabetes, immunocompromise, peripheral vascular disease, cirrhosis (Vibrio), and a perineal infection (Fournier)

Data

• This is a clinical and surgical diagnosis — do not delay surgery for tests

• Supportive labs: CBC, CMP, lactate, CRP, CK (muscle), coagulation studies, and blood cultures; the LRINEC score (an adjunct, not a rule-out)

• Imaging (CT/MRI — fascial gas and edema) only if it won't delay surgery in a stable patient

• Operative findings with a tissue Gram stain and culture confirm the diagnosis and guide therapy

DDx

Necrotizing soft tissue infection · severe cellulitis or erysipelas · an abscess · gas gangrene (clostridial myonecrosis) · pyomyositis · DVT · compartment syndrome · Fournier gangrene (the perineal subtype)

Home Meds

• NPO (emergent surgery); hold anticoagulants and oral agents pre-operatively

• Reconcile and renally dose antibiotics; provide aggressive resuscitation

• Stress-dose steroids if there is chronic use; hold metformin (AKI, lactic acidosis)

Plan

CONSULT: Surgery (emergent — immediate operative exploration and aggressive debridement; the priority, repeated as needed) · ICU (septic shock, resuscitation) · Infectious Disease (antibiotic tailoring, toxin management) · Urology/Gyn (Fournier) · Plastics (reconstruction afterward) · Hyperbaric (an adjunct at select centers)

• Emergent surgical debridement is the definitive, life-saving treatment — do not delay for imaging or labs: immediate operative exploration, aggressive excision of all necrotic tissue, planned repeat "second-look" debridements every 24 hours until there is no further necrosis, and amputation if the limb is non-salvageable; antibiotics and ICU support are adjuncts to surgery, never substitutes

• Broad empiric antibiotics immediately (covering gram-positives including MRSA, gram-negatives including Pseudomonas, anaerobes, and toxin; this formulary uses cefepime, not piperacillin-tazobactam):

• • Vancomycin IV (MRSA) plus cefepime 2 g IV every 8 hours (gram-negatives including Pseudomonas) plus metronidazole 500 mg IV every 8 hours (anaerobes — cefepime lacks anaerobic coverage, so add it; together replacing the broad single-agent role of Zosyn) plus clindamycin 900 mg IV every 8 hours

• • Clindamycin is added specifically to suppress toxin production (streptococcal and staphylococcal exotoxins — the "Eagle effect"; protein-synthesis inhibition reduces toxin even at high bacterial loads) — keep it on until the patient is clinically stable and the source is controlled

• Aggressive resuscitation and ICU: fluids, vasopressors, and organ support (the sepsis and septic shock pathway); these patients are critically ill

• Target once cultures and operative data return (narrow): Group A Strep → penicillin plus clindamycin; MRSA → continue vancomycin; Vibrio (water, cirrhosis) → doxycycline plus ceftriaxone or cefepime; Clostridium → penicillin plus clindamycin

• IVIG may be considered for streptococcal toxic shock or severe Group A Strep disease (an adjunct, per ID and critical care)

• Duration and step-down: continue IV until the source is controlled (no further necrosis on serial debridement), the patient is hemodynamically stable, afebrile, and improving — the duration is individualized (commonly continued for a period after the last debridement); step down to a culture-directed oral agent once the source is definitively controlled, off pressors, afebrile, and tolerating oral intake with an active oral option; clindamycin can stop once the patient is stable and the toxin risk has resolved

• PT/OT: later — extensive rehabilitation, wound care, reconstruction, and functional recovery after the debridements

• Trend: the wound and debridement margins (serial), hemodynamics and pressor needs, lactate, organ function, WBC and CK, cultures, and the response; with daily surgical reassessment

• Escalation triggers: ongoing necrosis → return to the OR (repeat debridement); refractory shock → ICU escalation; new compartment involvement → a fasciotomy or amputation decision; streptococcal toxic shock → IVIG; failure → ID and broaden or reassess

• Discharge checklist: the source definitively controlled (no further necrosis), hemodynamically stable, with wounds managed; an oral or IV regimen with the total duration and stop date specified, culture-directed; an extensive wound-care and reconstruction plan; surgery, ID, plastics, and rehabilitation follow-up; nutrition optimization; diabetes and underlying-condition management; return precautions for recurrent fever, wound deterioration or new necrosis, spreading pain or redness, or systemic illness

Red Flags

• Pain out of proportion to an unimpressive exam in a toxic patient → necrotizing infection; emergent surgical consult

• Any delay of surgery for imaging or a LRINEC score → raises mortality; explore now

• Crepitus, hemorrhagic bullae, skin anesthesia, or "dishwater" drainage → late, ominous signs; the OR is overdue

• Septic shock → aggressive ICU resuscitation alongside debridement

• Streptococcal toxic shock → add clindamycin and consider IVIG

Senior IM Resident Pearls

• Suspicion means the OR. Surgery both confirms necrotizing infection and saves the patient — every hour of delay for a CT or a LRINEC score raises mortality.

• Pain out of proportion is the early tell. An unimpressive-looking exam in a toxic patient precedes the dramatic skin findings — believe the pain.

• Clindamycin earns its place by suppressing toxin. It shuts down the streptococcal and staphylococcal exotoxins driving the shock, even at high bacterial loads.

• Cefepime needs metronidazole here too. The broad regimen is vancomycin plus cefepime plus metronidazole plus clindamycin, since cefepime alone misses anaerobes.

• Plan to go back daily. Second-look debridements every 24 hours until the necrosis stops are the rule, not the exception.

• Think Vibrio in the cirrhotic with water exposure. Seawater or raw shellfish in a liver patient changes the coverage to include doxycycline.

• Common mistake: treating early necrotizing infection as cellulitis and "observing" — that delay, waiting for the skin to declare itself, is what turns a salvageable limb into a fatal sepsis.

Infectious Disease — Mycobacterial

124. Tuberculosis

pulmonary TB · reactivation disease · AIRBORNE ISOLATION + 3 sputum AFB/NAAT · RIPE × 2 months then RI × 4 months (6 mo total) · DOT + public-health reporting · Super Compact

Sx: chronic cough (>2–3 weeks), hemoptysis, fever, drenching night sweats, weight loss, anorexia, fatigue (subacute/chronic course); reactivation favors upper lobes/apical · extrapulmonary: lymphadenitis, pleural, CNS (meningitis), spinal (Pott), miliary (disseminated) · (the combination of weeks of cough, weight loss, and night sweats — especially with apical/cavitary changes or risk factors — should trigger AIRBORNE ISOLATION first and questions later; protecting staff/other patients comes before the workup)

Neg: denies failure to isolate on suspicion (airborne precautions immediately — don't wait for confirmation) · denies missing HIV co-testing (changes management, common coinfection) · denies missed drug resistance (MDR/XDR — prior treatment, exposure, non-response) · denies missed extrapulmonary/disseminated disease · denies missed latent-vs-active distinction · denies hepatotoxicity monitoring lapse

SHx: TB exposure/contacts, prior TB/treatment (resistance, incomplete therapy), birth/residence/travel in high-burden region, HIV/immunocompromise (TNF inhibitors, transplant, steroids), homelessness/incarceration/congregate living, healthcare work, substance use, diabetes, malnutrition, prior positive TST/IGRA

Etiology: Mycobacterium tuberculosis, airborne (droplet nuclei) · primary infection often contained as latent TB (asymptomatic, non-infectious); reactivation when immunity wanes (HIV, age, immunosuppression, diabetes) → active, infectious pulmonary disease, classically upper-lobe/cavitary · slow-growing → indolent presentation + long treatment

RF: exposure/high-burden origin · HIV/immunocompromise · prior incomplete treatment (resistance) · congregate living (shelter/prison) · diabetes · malnutrition · substance use · age

Data: AIRBORNE ISOLATION (negative-pressure room) + ≥3 sputum specimens for AFB smear + mycobacterial culture + NAAT (rapid molecular — also detects rifampin resistance) · CXR (upper-lobe infiltrates/cavitation in reactivation; hilar adenopathy/effusion); CT for detail · HIV test (mandatory), CBC, CMP, baseline LFTs (hepatotoxic drugs), visual acuity/color (ethambutol); TST/IGRA (latent, not for active rule-out); drug-susceptibility testing

DDx: active pulmonary TB · latent TB (asymptomatic — different management) · bacterial/fungal pneumonia · lung malignancy · nontuberculous mycobacteria · sarcoidosis · lung abscess · other cavitary disease

Home Meds: reconcile (multiple DDIs — rifampin is a potent CYP inducer: reduces warfarin, contraceptives, many ARVs, methadone, etc.); renally/hepatically adjust; add pyridoxine (B6) with isoniazid (prevent neuropathy); monitor LFTs; HIV ART coordination (timing/IRIS) with ID

Plan

CONSULT: Infectious Disease (regimen, resistance, HIV co-management, complex/extrapulmonary — essential) · Public Health/TB Control (mandatory reporting, contact investigation, DOT) · Pulmonary (diagnostic bronchoscopy if sputum-negative + high suspicion) · HIV/ID (coinfection, ART timing)

– AIRBORNE ISOLATION immediately on suspicion (negative-pressure room, N95/respirator) — maintain until criteria for non-infectiousness met (clinical improvement on therapy + serial negative AFB smears) — protects others first
– STANDARD REGIMEN for drug-susceptible active TB — "RIPE" (intensive phase 2 months, then continuation 4 months = 6 months total):
  • INTENSIVE PHASE (first 2 months): Rifampin + Isoniazid (+ Pyridoxine/B6) + Pyrazinamide + Ethambutol — all four daily
  • CONTINUATION PHASE (next 4 months): Rifampin + Isoniazid (+ pyridoxine) — drop pyrazinamide + ethambutol once susceptibility confirms pan-susceptible
  (typical adult dosing examples — weight-based, confirm: isoniazid 5 mg/kg ~300 mg, rifampin 10 mg/kg ~600 mg, pyrazinamide ~25 mg/kg, ethambutol ~15–20 mg/kg, daily; pyridoxine 25–50 mg daily)
  • Longer courses for: cavitary + positive 2-month culture, CNS TB (≥9–12 mo + steroids), bone/joint, disseminated — ID-directed
– DOT (Directly Observed Therapy) via public health — the standard of care to ensure adherence + prevent resistance + relapse
– DRUG-RESISTANT TB (MDR/XDR): if rifampin resistance on NAAT or risk factors → ID/TB expert, individualized multidrug regimen (longer, alternative agents) — do not use the standard regimen alone
– HIV testing mandatory; coordinate ART timing (IRIS risk) with ID; co-manage immunosuppression
– MONITORING: baseline + serial LFTs (hepatotoxicity — isoniazid/rifampin/pyrazinamide), visual acuity + color vision (ethambutol — optic neuritis), monthly sputum cultures (confirm conversion), adherence, symptom response, drug interactions
– STEP-DOWN note: TB therapy is oral throughout (no IV→PO concept) — the "phases" are the analogous structure; the key transition is intensive (4 drugs) → continuation (2 drugs) after culture confirms susceptibility; total 6 months for standard drug-susceptible pulmonary TB
– Two reflexes define inpatient TB. First, isolate on suspicion — the negative-pressure room and N95 go up before the workup, because protecting staff and other patients can't wait for confirmation. Second, remember the structure and the letters: RIPE for two months, then rifampin and isoniazid for four more, six months total for drug-susceptible disease — and always pair isoniazid with B6 to prevent the neuropathy. Three things you can't skip: test for HIV in every case, send a rapid molecular test that also flags rifampin resistance, and report to public health so contact tracing and directly observed therapy happen. Watch the liver and the eyes while they're on treatment.
– PT/OT: nutritional rehab (often malnourished); pulmonary rehab if significant disease
– Trend: symptoms/weight, sputum smear + culture conversion (monthly), LFTs, visual function (ethambutol), adherence, drug interactions, CXR response
– Escalation triggers: drug resistance/non-conversion → TB expert + regimen change; hepatotoxicity (rising LFTs/symptoms) → hold/modify per protocol + ID; CNS/disseminated/severe → admit + extended therapy + steroids (TB meningitis/pericarditis); HIV coinfection complexity → ID
– Discharge checklist: isolation criteria for discharge met (or appropriate home isolation arranged) + on the full regimen; complete 6-month plan (RIPE→RI) with phase transitions + total duration specified; DOT + public-health linkage established, contacts being investigated; LFT + visual monitoring schedule; HIV result/ART plan; medication-interaction + adherence counseling; pyridoxine prescribed; ID + TB-clinic follow-up; return precautions (worsening symptoms, hemoptysis, jaundice/RUQ pain — hepatotoxicity, vision changes, drug intolerance)

124. Tuberculosis

complete reference · pulmonary + reactivation · airborne isolation, 3 sputum AFB/NAAT, RIPE → RI (6 months), DOT + public-health reporting · Full Card

Symptoms / Associated Sx

• Chronic cough (over 2–3 weeks), hemoptysis, fever, drenching night sweats, weight loss, anorexia, and fatigue (a subacute or chronic course); reactivation favors the upper lobes and apices

• Extrapulmonary disease: lymphadenitis, pleural disease, CNS (meningitis), spinal (Pott disease), and miliary (disseminated) disease

• The combination of weeks of cough, weight loss, and night sweats — especially with apical or cavitary changes or risk factors — should trigger airborne isolation first and questions later; protecting staff and other patients comes before the workup

Neg

• Pt denies a failure to isolate on suspicion (airborne precautions immediately — don't wait for confirmation)

• Pt denies missing HIV co-testing (it changes management and is a common coinfection) and a missed drug resistance (MDR/XDR — prior treatment, exposure, non-response)

• Pt denies a missed extrapulmonary or disseminated disease, a missed latent-versus-active distinction, and a hepatotoxicity monitoring lapse

Social History (SHx)

• TB exposure or contacts, prior TB or treatment (resistance, incomplete therapy), and birth, residence, or travel in a high-burden region

• HIV or immunocompromise (TNF inhibitors, transplant, steroids), and homelessness, incarceration, or congregate living

• Healthcare work, substance use, diabetes, malnutrition, and a prior positive TST or IGRA

Main Etiology

• Mycobacterium tuberculosis, airborne (droplet nuclei)

• Primary infection is often contained as latent TB (asymptomatic, non-infectious); reactivation occurs when immunity wanes (HIV, age, immunosuppression, diabetes), producing active, infectious pulmonary disease, classically upper-lobe and cavitary

• It is slow-growing, hence the indolent presentation and long treatment

RF

• Modifiable: incomplete prior treatment (resistance), congregate living, substance use, and malnutrition

• Non-modifiable: exposure or high-burden origin, HIV or immunocompromise, diabetes, and age

Data

• Airborne isolation (a negative-pressure room) with at least 3 sputum specimens for AFB smear, mycobacterial culture, and NAAT (a rapid molecular test that also detects rifampin resistance)

• CXR (upper-lobe infiltrates and cavitation in reactivation; hilar adenopathy or effusion); CT for detail

• An HIV test (mandatory), CBC, CMP, baseline LFTs (hepatotoxic drugs), and visual acuity and color vision (ethambutol)

• TST or IGRA (for latent disease, not to rule out active disease); and drug-susceptibility testing

DDx

Active pulmonary TB · latent TB (asymptomatic — different management) · bacterial or fungal pneumonia · lung malignancy · nontuberculous mycobacteria · sarcoidosis · a lung abscess · other cavitary disease

Home Meds

• Reconcile (multiple drug interactions — rifampin is a potent CYP inducer that reduces warfarin, contraceptives, many antiretrovirals, methadone, and others)

• Adjust renally and hepatically; add pyridoxine (B6) with isoniazid (preventing neuropathy)

• Monitor LFTs and coordinate HIV ART (timing, IRIS) with ID

Plan

CONSULT: Infectious Disease (regimen, resistance, HIV co-management, complex or extrapulmonary disease — essential) · Public Health/TB Control (mandatory reporting, contact investigation, DOT) · Pulmonary (diagnostic bronchoscopy if sputum-negative with high suspicion) · HIV/ID (coinfection, ART timing)

• Airborne isolation immediately on suspicion (a negative-pressure room, N95 or respirator) — maintained until criteria for non-infectiousness are met (clinical improvement on therapy with serial negative AFB smears) — protecting others first

• Standard regimen for drug-susceptible active TB — "RIPE" (an intensive phase of 2 months, then a continuation phase of 4 months = 6 months total):

• • Intensive phase (the first 2 months): Rifampin plus Isoniazid (plus Pyridoxine/B6) plus Pyrazinamide plus Ethambutol — all four daily

• • Continuation phase (the next 4 months): Rifampin plus Isoniazid (plus pyridoxine) — dropping pyrazinamide and ethambutol once susceptibility confirms pan-susceptible disease

• • Typical adult dosing examples (weight-based, confirm): isoniazid 5 mg/kg (~300 mg), rifampin 10 mg/kg (~600 mg), pyrazinamide ~25 mg/kg, ethambutol ~15–20 mg/kg daily; pyridoxine 25–50 mg daily

• • Longer courses for: cavitary disease with a positive 2-month culture, CNS TB (≥9–12 months with steroids), and bone/joint or disseminated disease — ID-directed

• DOT (directly observed therapy) via public health — the standard of care to ensure adherence and prevent resistance and relapse

• Drug-resistant TB (MDR/XDR): if there is rifampin resistance on NAAT or risk factors → an ID/TB expert and an individualized multidrug regimen (longer, alternative agents) — do not use the standard regimen alone

• HIV testing is mandatory; coordinate ART timing (IRIS risk) with ID and co-manage immunosuppression

• Monitoring: baseline and serial LFTs (hepatotoxicity — isoniazid, rifampin, pyrazinamide), visual acuity and color vision (ethambutol — optic neuritis), monthly sputum cultures (confirming conversion), adherence, the symptom response, and drug interactions

• Step-down note: TB therapy is oral throughout (there is no IV→PO concept) — the "phases" are the analogous structure; the key transition is intensive (4 drugs) → continuation (2 drugs) after culture confirms susceptibility; the total is 6 months for standard drug-susceptible pulmonary TB

• PT/OT: nutritional rehabilitation (patients are often malnourished); pulmonary rehabilitation if significant disease

• Trend: symptoms and weight, sputum smear and culture conversion (monthly), LFTs, visual function (ethambutol), adherence, drug interactions, and the CXR response

• Escalation triggers: drug resistance or non-conversion → a TB expert and a regimen change; hepatotoxicity (rising LFTs or symptoms) → hold or modify per protocol with ID; CNS, disseminated, or severe disease → admission, extended therapy, and steroids (TB meningitis, pericarditis); HIV coinfection complexity → ID

• Discharge checklist: isolation criteria for discharge met (or appropriate home isolation arranged) and on the full regimen; the complete 6-month plan (RIPE → RI) with phase transitions and total duration specified; DOT and public-health linkage established with contacts being investigated; an LFT and visual monitoring schedule; the HIV result and ART plan; medication-interaction and adherence counseling; pyridoxine prescribed; ID and TB-clinic follow-up; return precautions for worsening symptoms, hemoptysis, jaundice or RUQ pain (hepatotoxicity), vision changes, or drug intolerance

Red Flags

• Failure to isolate on suspicion → airborne precautions go up before confirmation to protect staff and patients

• Rifampin resistance on NAAT or risk factors → MDR/XDR TB; a TB expert and an individualized regimen, not the standard one

• Rising LFTs or hepatitis symptoms → drug-induced hepatotoxicity; hold and modify per protocol

• Vision or color changes → ethambutol optic neuritis

• HIV coinfection → mandatory testing with careful ART timing (IRIS risk)

Senior IM Resident Pearls

• Isolate on suspicion. The negative-pressure room and N95 go up before the workup — protecting staff and other patients can't wait for confirmation.

• Remember the structure and the letters. RIPE for two months, then rifampin and isoniazid for four more — six months total for drug-susceptible disease.

• Always pair isoniazid with B6. Pyridoxine prevents the peripheral neuropathy isoniazid otherwise causes.

• Three things you can't skip: test for HIV in every case, send a rapid molecular test that flags rifampin resistance, and report to public health for contact tracing and DOT.

• Watch the liver and the eyes. Serial LFTs catch hepatotoxicity, and visual acuity and color vision catch ethambutol optic neuritis.

• DOT is the standard. Directly observed therapy is how you ensure adherence and prevent the resistance and relapse that incomplete courses breed.

• Common mistake: using a positive TST/IGRA to "rule out" active TB — those tests confirm exposure, not activity, and active disease still needs sputum, imaging, and isolation.

Infectious Disease — Immunocompromised Host

125. Opportunistic Infections in Immunocompromised Patients

HIV/AIDS · transplant recipients · chemotherapy patients · risk by net immunosuppression + CD4 · PJP, CMV, cryptococcus, MAC, fungal · prophylaxis + restore immunity · Super Compact

Sx: infection presentations blunted/atypical by immunosuppression (muted fever/inflammation) · PJP: subacute dyspnea, dry cough, hypoxia (esp exertional), often subtle CXR vs marked hypoxia · cryptococcal meningitis: headache, fever, AMS (indolent) · CMV: retinitis (vision), colitis, pneumonitis · candidiasis: thrush, esophagitis (odynophagia) · disseminated fungal/MAC: fevers, wasting, cytopenias · (in the immunocompromised, the degree of net immunosuppression and the CD4 count tell you WHICH opportunists to fear — match the workup and empiric therapy to the specific defect, and don't be reassured by a blunted presentation)

Neg: denies missing PJP in a hypoxic immunocompromised patient (start treatment + steroids early) · denies missing cryptococcal meningitis (LP + opening pressure) · denies missing CMV (retinitis → blindness, colitis) · denies failing to assess net immunosuppression/CD4 to scope the differential · denies missed prophylaxis gaps · denies missed IRIS · denies neutropenic fever mismanagement

SHx: type + degree of immunosuppression: HIV (CD4 count, viral load, ART adherence, OI prophylaxis status), transplant (organ, time since — early bacterial/nosocomial vs later opportunistic, net immunosuppression, rejection treatment), chemo/malignancy (neutropenia, agents — anti-CD20/T-cell-depleting), steroids/biologics, prior OIs, exposures/travel/TB

Etiology: defect determines organism: T-cell/CD4 deficiency (HIV/AIDS, transplant, steroids) → PJP, cryptococcus, CMV, MAC, Toxoplasma, candidiasis, TB · neutropenia (chemo) → bacterial sepsis, invasive fungal (Aspergillus, Candida) · B-cell/humoral/anti-CD20 → encapsulated bacteria, enteroviruses · HIV CD4 thresholds: <200 (PJP), <100 (toxo, cryptococcus, esophageal candida), <50 (CMV, disseminated MAC)

RF: low CD4/advanced HIV · transplant immunosuppression · neutropenia/chemo · high-dose steroids/biologics · poor prophylaxis adherence · prior OI

Data: HIV CD4 + viral load (if HIV); assess net immunosuppression · targeted by syndrome: PJP → hypoxia/A-a gradient, LDH, induced sputum/BAL (PCP PCR, stain), CT (ground-glass); cryptococcus → serum cryptococcal antigen, LP (opening pressure, CrAg, culture, India ink); CMV → CMV PCR/viral load, tissue biopsy, dilated fundoscopy (retinitis); fungal → blood cultures, beta-D-glucan, galactomannan, CT; blood cultures + broad workup; toxo serology/MRI brain

DDx: by syndrome — pulmonary (PJP vs bacterial/viral/fungal pneumonia vs TB) · CNS (cryptococcus vs toxo vs CNS lymphoma vs PML) · GI (CMV vs candida vs C. diff) · febrile neutropenia (bacterial vs fungal) · disseminated (MAC, fungal, TB) · drug toxicity/malignancy mimics

Home Meds: continue/optimize ART (HIV) — coordinate timing with OI treatment (IRIS); adjust transplant immunosuppression with transplant team (often reduce during severe infection); reconcile DDIs (azoles + many drugs, rifampin); renally dose; continue/restart appropriate OI prophylaxis

Plan

CONSULT: Infectious Disease (essential — diagnosis, OI-specific therapy, prophylaxis, complex hosts) · HIV specialist (ART, IRIS) · Transplant team (immunosuppression adjustment) · Oncology/Heme (neutropenic fever, chemo) · Ophthalmology (CMV retinitis) · Pulmonary (BAL)

– SCOPE THE DIFFERENTIAL by the immune defect + CD4/net immunosuppression, then target diagnosis + empiric therapy to the syndrome; broad cultures + specific OI testing
– PJP (Pneumocystis jirovecii) pneumonia: TMP-SMX (high-dose, ~15–20 mg/kg/day of TMP component IV/PO divided) × 21 days; ADD corticosteroids (prednisone taper) if moderate-severe — PaO2 <70 mmHg on room air OR A-a gradient ≥35 (reduces mortality/respiratory failure) — give steroids before/with antibiotics
– Cryptococcal meningitis: induction amphotericin B (liposomal) + flucytosine, then consolidation/maintenance fluconazole; manage raised ICP with serial therapeutic LPs (a key survival determinant)
– CMV (retinitis/colitis/pneumonitis): ganciclovir IV (or valganciclovir PO) per disease/severity; urgent ophthalmology for retinitis
– Disseminated MAC: clarithromycin/azithromycin + ethambutol (± rifabutin); invasive aspergillosis → voriconazole; candidiasis → echinocandin/fluconazole; toxoplasmosis → pyrimethamine + sulfadiazine + leucovorin
– FEBRILE NEUTROPENIA (chemo): emergency — broad empiric antibiotics immediately: cefepime 2 g IV q8h (antipseudomonal monotherapy on THIS formulary, replacing piperacillin-tazobactam); add vancomycin for specific indications (line, skin/soft-tissue, unstable, MRSA risk); add antifungal if persistent fever/fungal risk — per neutropenic-fever protocol + ID
– RESTORE IMMUNITY (the long-term cure): start/optimize ART in HIV (coordinate timing to balance OI control vs IRIS — ID/HIV-guided), reduce transplant immunosuppression where safe (transplant team), recover neutrophils (chemo timing ± G-CSF)
– PROPHYLAXIS (prevent the next OI; CD4-driven in HIV): PJP prophylaxis (TMP-SMX) when CD4 <200; toxoplasmosis prophylaxis CD4 <100 (TMP-SMX covers both); MAC historically CD4 <50 (now often deferred if rapid ART) — per current guidelines; transplant/chemo prophylaxis per protocols (e.g. PJP prophylaxis on chronic steroids/certain regimens)
– The organizing principle is simple: the immune defect picks the pathogen. A CD4 count or the net immunosuppression tells you which opportunists to fear and lets you match both the workup and empiric therapy to the specific gap — and because presentations are blunted, you trust the risk profile over a reassuring exam. A few high-yield reflexes: any hypoxic immunocompromised patient with ground-glass on CT gets PJP treatment plus steroids if the oxygenation is poor (PaO2 under 70 or A-a gradient 35+); cryptococcal meningitis lives or dies by controlling the intracranial pressure with repeated LPs; and febrile neutropenia is an emergency that gets cefepime within the hour. But the real cure is restoring the immune system — ART, dialing back immunosuppression, neutrophil recovery — and then keeping the next infection away with CD4-driven prophylaxis.
– PT/OT: nutritional + functional rehab; deconditioning common in prolonged immunosuppression
– Trend: oxygenation (PJP), ICP/LP (cryptococcus), CMV viral load/vision, neutrophil count, CD4/viral load, response to OI therapy, IRIS signs, drug levels/toxicity
– Escalation triggers: respiratory failure (PJP) → ICU; raised ICP/declining mentation (crypto) → urgent LP/CSF diversion + neuro; CMV retinitis → emergent ophtho; febrile neutropenia instability → ICU + broaden; IRIS → ID; multiple/refractory OIs → ID-led multidisciplinary
– Discharge checklist: OI treated/controlled + immunosuppression addressed (ART started/optimized, transplant meds adjusted, counts recovering); OI-specific regimen with total duration/maintenance plan + stop/transition date specified; appropriate OI prophylaxis prescribed (CD4-driven) + adherence counseling; ID + HIV/transplant/onc follow-up; drug-interaction counseling; vaccination review (appropriate to host); return precautions (worsening dyspnea/hypoxia, headache/confusion, vision changes, fever esp if neutropenic, new focal symptoms)

125. Opportunistic Infections in Immunocompromised Patients

complete reference · HIV/AIDS + transplant + chemotherapy · defect-driven differential, syndrome-targeted therapy, restore immunity + prophylaxis · Full Card

Symptoms / Associated Sx

• Infection presentations are blunted and atypical from immunosuppression (muted fever and inflammation)

• PJP: subacute dyspnea, dry cough, and hypoxia (especially exertional), often with a subtle CXR despite marked hypoxia

• Cryptococcal meningitis: headache, fever, and altered mental status (indolent); CMV: retinitis (vision), colitis, and pneumonitis; candidiasis: thrush and esophagitis (odynophagia); disseminated fungal or MAC disease: fevers, wasting, and cytopenias

• In the immunocompromised, the degree of net immunosuppression and the CD4 count tell you which opportunists to fear — match the workup and empiric therapy to the specific defect, and don't be reassured by a blunted presentation

Neg

• Pt denies missing PJP in a hypoxic immunocompromised patient (start treatment and steroids early) and missing cryptococcal meningitis (LP with an opening pressure)

• Pt denies missing CMV (retinitis → blindness, colitis) and failing to assess net immunosuppression or CD4 to scope the differential

• Pt denies missed prophylaxis gaps, a missed IRIS, and neutropenic fever mismanagement

Social History (SHx)

• The type and degree of immunosuppression: HIV (CD4 count, viral load, ART adherence, OI prophylaxis status)

• Transplant (the organ, time since — early bacterial/nosocomial versus later opportunistic, net immunosuppression, rejection treatment)

• Chemotherapy or malignancy (neutropenia, the agents — anti-CD20 or T-cell-depleting), steroids or biologics, prior OIs, and exposures, travel, or TB

Main Etiology

• The defect determines the organism: T-cell/CD4 deficiency (HIV/AIDS, transplant, steroids) → PJP, cryptococcus, CMV, MAC, Toxoplasma, candidiasis, and TB

• Neutropenia (chemotherapy) → bacterial sepsis and invasive fungal disease (Aspergillus, Candida); B-cell/humoral or anti-CD20 deficiency → encapsulated bacteria and enteroviruses

• HIV CD4 thresholds: below 200 (PJP), below 100 (toxoplasmosis, cryptococcus, esophageal candidiasis), and below 50 (CMV, disseminated MAC)

RF

• Modifiable: poor prophylaxis adherence and ART non-adherence

• Non-modifiable: a low CD4 or advanced HIV, transplant immunosuppression, neutropenia or chemotherapy, high-dose steroids or biologics, and a prior OI

Data

• HIV CD4 and viral load (if HIV); assess the net immunosuppression

• Targeted by syndrome: PJP → hypoxia and A-a gradient, LDH, induced sputum or BAL (PCP PCR, stain), CT (ground-glass); cryptococcus → serum cryptococcal antigen, LP (opening pressure, CrAg, culture, India ink); CMV → CMV PCR or viral load, tissue biopsy, dilated fundoscopy (retinitis); fungal → blood cultures, beta-D-glucan, galactomannan, CT

• Blood cultures with a broad workup; toxoplasmosis serology and MRI brain

DDx

By syndrome — pulmonary (PJP versus bacterial, viral, or fungal pneumonia versus TB) · CNS (cryptococcus versus toxoplasmosis versus CNS lymphoma versus PML) · GI (CMV versus candidiasis versus C. difficile) · febrile neutropenia (bacterial versus fungal) · disseminated disease (MAC, fungal, TB) · drug toxicity or malignancy mimics

Home Meds

• Continue and optimize ART (HIV) — coordinating timing with OI treatment (IRIS)

• Adjust transplant immunosuppression with the transplant team (often reducing it during severe infection)

• Reconcile drug interactions (azoles with many drugs, rifampin), dose renally, and continue or restart appropriate OI prophylaxis

Plan

CONSULT: Infectious Disease (essential — diagnosis, OI-specific therapy, prophylaxis, complex hosts) · HIV specialist (ART, IRIS) · Transplant team (immunosuppression adjustment) · Oncology/Heme (neutropenic fever, chemotherapy) · Ophthalmology (CMV retinitis) · Pulmonary (BAL)

• Scope the differential by the immune defect and CD4 or net immunosuppression, then target the diagnosis and empiric therapy to the syndrome; broad cultures plus specific OI testing

• PJP (Pneumocystis jirovecii) pneumonia: TMP-SMX (high-dose, ~15–20 mg/kg/day of the TMP component IV/PO divided) for 21 days; add corticosteroids (a prednisone taper) if moderate-to-severe — a PaO2 below 70 mmHg on room air or an A-a gradient ≥35 (this reduces mortality and respiratory failure) — give steroids before or with the antibiotics

• Cryptococcal meningitis: induction with liposomal amphotericin B plus flucytosine, then consolidation and maintenance with fluconazole; manage raised ICP with serial therapeutic LPs (a key survival determinant)

• CMV (retinitis, colitis, pneumonitis): ganciclovir IV (or valganciclovir PO) per the disease and severity; urgent ophthalmology for retinitis

• Disseminated MAC: clarithromycin or azithromycin plus ethambutol (with rifabutin); invasive aspergillosis → voriconazole; candidiasis → an echinocandin or fluconazole; toxoplasmosis → pyrimethamine plus sulfadiazine plus leucovorin

• Febrile neutropenia (chemotherapy): an emergency — broad empiric antibiotics immediately: cefepime 2 g IV every 8 hours (antipseudomonal monotherapy on this formulary, replacing piperacillin-tazobactam); add vancomycin for specific indications (a line, skin/soft-tissue infection, instability, MRSA risk); add an antifungal if there is persistent fever or fungal risk — per the neutropenic-fever protocol and ID

• Restore immunity (the long-term cure): start or optimize ART in HIV (coordinating timing to balance OI control against IRIS — ID/HIV-guided), reduce transplant immunosuppression where safe (the transplant team), and recover neutrophils (chemotherapy timing, with G-CSF)

• Prophylaxis (preventing the next OI; CD4-driven in HIV): PJP prophylaxis (TMP-SMX) when CD4 is below 200; toxoplasmosis prophylaxis when CD4 is below 100 (TMP-SMX covers both); MAC prophylaxis historically when CD4 is below 50 (now often deferred with rapid ART) — per current guidelines; transplant and chemotherapy prophylaxis per protocols (e.g. PJP prophylaxis on chronic steroids or certain regimens)

• PT/OT: nutritional and functional rehabilitation; deconditioning is common in prolonged immunosuppression

• Trend: oxygenation (PJP), ICP and LP (cryptococcus), CMV viral load and vision, the neutrophil count, CD4 and viral load, the response to OI therapy, IRIS signs, and drug levels and toxicity

• Escalation triggers: respiratory failure (PJP) → ICU; raised ICP or declining mentation (cryptococcus) → urgent LP or CSF diversion and neurology; CMV retinitis → emergent ophthalmology; febrile neutropenia with instability → ICU and broaden; IRIS → ID; multiple or refractory OIs → ID-led multidisciplinary care

• Discharge checklist: the OI treated or controlled with immunosuppression addressed (ART started or optimized, transplant medications adjusted, counts recovering); the OI-specific regimen with the total duration or maintenance plan and a stop or transition date specified; appropriate OI prophylaxis prescribed (CD4-driven) with adherence counseling; ID and HIV/transplant/oncology follow-up; drug-interaction counseling; a vaccination review (appropriate to the host); return precautions for worsening dyspnea or hypoxia, headache or confusion, vision changes, fever (especially if neutropenic), or new focal symptoms

Red Flags

• A hypoxic immunocompromised patient with ground-glass on CT → PJP; treat plus add steroids if the PaO2 is below 70 or the A-a gradient is ≥35

• Cryptococcal meningitis → control the intracranial pressure with serial LPs; it's a key survival determinant

• Febrile neutropenia → an emergency; broad antibiotics (cefepime) within the hour

• CMV retinitis → emergent ophthalmology to prevent blindness

• IRIS after starting ART → a paradoxical worsening that needs ID management, not necessarily stopping ART

Senior IM Resident Pearls

• The immune defect picks the pathogen. A CD4 count or the net immunosuppression tells you which opportunists to fear and lets you match both the workup and empiric therapy to the specific gap.

• Trust the risk profile over the exam. Presentations are blunted, so a reassuring appearance in a profoundly immunosuppressed patient doesn't exclude serious infection.

• PJP with poor oxygenation gets steroids. A PaO2 below 70 or an A-a gradient of 35 or more is the trigger to add corticosteroids before or with TMP-SMX.

• Cryptococcal meningitis lives or dies on the pressure. Serial therapeutic LPs to control intracranial pressure matter as much as the antifungal.

• Febrile neutropenia is an emergency. Cefepime within the hour — this is the local antipseudomonal monotherapy in place of Zosyn.

• The cure is restoring immunity. ART, dialing back immunosuppression, and neutrophil recovery do what antibiotics alone can't — and then prophylaxis keeps the next OI away.

• Common mistake: treating the infection but forgetting to set up CD4-driven prophylaxis and immune restoration — without those, the patient simply returns with the next opportunist.