Community acquired pneumonia


Symptoms / Associated Sx

  • Fever, chills, rigors

  • Productive cough (purulent sputum — typical bacterial; dry cough — atypical/viral)

  • Pleuritic chest pain (pleural involvement)

  • Dyspnea, tachypnea, hypoxia

  • Tachycardia, hypotension (severe/septic)

  • Decreased breath sounds, dullness to percussion, bronchial breath sounds, egophony (consolidation)

  • Confusion (elderly — altered mentation as the only presenting sign)

Denies

  • Recent hospitalization or healthcare exposure within 90 days (rules out HAP/HCAP — changes antibiotic coverage)

  • Known aspiration event, dysphagia (rules out aspiration pneumonia)

  • Immunosuppression (rules out PCP, fungal pneumonia, atypical pathogens)

  • Travel to endemic areas (rules out coccidioidomycosis, histoplasmosis, Legionella endemic)

Social History (SHx)

Smoking (impairs mucociliary clearance), alcohol use (aspiration risk, S. pneumoniae), COPD, prior pneumonia, recent viral illness, close contacts with illness, nursing home residence, recent travel, immunosuppression, vaccination history (pneumococcal, influenza).

Main Etiology

  • Typical bacteria: Streptococcus pneumoniae (most common overall), Staphylococcus aureus, Haemophilus influenzae, Klebsiella pneumoniae (alcoholics)

  • Atypical organisms: Mycoplasma pneumoniae (young adults, walking pneumonia), Chlamydophila pneumoniae, Legionella pneumophila (water exposure, severe CAP)

  • Viral: Influenza A/B, RSV, SARS-CoV-2, adenovirus, parainfluenza

  • Aspiration CAP: oral anaerobes, gram-negatives in healthcare-associated

Most Common DDx

  • Acute decompensated heart failure (bilateral symmetric infiltrates; elevated BNP; peripheral edema; JVD; responds to diuretics not antibiotics)

  • COPD exacerbation (known COPD; increased dyspnea + sputum; no focal consolidation; hyperinflation on CXR; responds to bronchodilators)

  • Pulmonary embolism (dyspnea + pleuritic pain; hypoxia; no fever or infiltrate early; D-dimer + CTPA; Hampton's hump on CXR rarely)

  • Lung cancer with post-obstructive pneumonia (recurrent pneumonia same lobe; mass on CT; weight loss; smoking history)

  • Pulmonary hemorrhage / DAH (hemoptysis + bilateral infiltrates; no fever; rheumatologic history; ANCA/anti-GBM)

  • Acute eosinophilic pneumonia (dyspnea + bilateral infiltrates; eosinophilia on BAL; recent new exposure; responds to steroids not antibiotics)

DATA

  • CBC (leukocytosis with left shift — bacterial; leukopenia in severe sepsis or viral)

  • BMP (creatinine — severity; glucose; electrolytes)

  • LFTs (Legionella — elevated; sepsis)

  • Procalcitonin (>0.25 ng/mL supports bacterial; guide antibiotic duration)

  • Blood cultures × 2 (before antibiotics — positive in ~10% of hospitalized CAP; guides narrowing)

  • Sputum Gram stain + culture (before antibiotics; quality matters — >25 PMN, <10 epithelial cells)

  • Urinary antigens: Legionella (serogroup 1 — most common; detects 70–80% of cases) and pneumococcal (sensitive and specific)

  • Viral respiratory panel (influenza, RSV, COVID-19, parainfluenza)

  • CXR (infiltrate pattern — lobar: typical bacterial; interstitial/bilateral: viral/atypical; cavitation: S. aureus, anaerobes, TB)

  • CT chest (if CXR negative but high suspicion; characterize better; rule out obstruction)

  • ABG or VBG (if O2 <90% or dyspneic)

  • PSI/PORT score or CURB-65 (severity scoring — guides inpatient vs. outpatient decision)

  • HIV test (if risk factors or severe/atypical presentation)

Home Meds

  • Inhalers (COPD — continue; may reduce bronchospasm component)

  • ACE inhibitors (angiotensin II promotes aspiration — continue; cough may mask aspiration)

  • Immunosuppressants (steroids, biologics — increase infection risk; assess dose)

  • Prior antibiotic exposure within 3 months (adjust empiric therapy to avoid resistance)

Plan (PNA ADD ON)

  • CTX 2g total 5 days (date***)

  • Azithro 500 mg total 3 days (date***)

  • Severe → cefepime + vancomycin + Azithro

  • Aspiration concern → Ampicillin-sulbactam (Unasyn) + Azithro

  • HAP -> Cefepime + Vancomycin (≥48 hours after hospital admission)

  • f/u cultures

  • trend CBC,RFP daily

  • if not improving 48–72 hrs consider adding vanc + cefepime, CT chest/contrast and Cx if not drawn

  • Supportive: acetaminophen PRN, incentive spirometry,

  • hydrocort 50 q6 or prednisone 50 PO daily if sepsis/shock or severe PNA, 4 to 7 days followed by a taper if Course >7 days

  • Afebrile ≥48 hrs and clinically stable → switch to PO: if on CTX + Azithro, change to Amoxicillin 875 mg PO BID and continue Azithro to complete 3 days total. If treated with FQ or for Pseudomonas, switch to Levofloxacin 750 mg PO daily or Ciprofloxacin 750 mg PO BID for 7 days total. If MRSA, use Linezolid 600 mg PO BID for 7–14 days total depending on severity/bacteremia.

  • f/u with PCP in one week after DC

-- Source Control: large parapneumonic effusions and any empyemas will need to be drained via thoracentesis; consider if >10mm, > half hemithorax, suspected to be causing dyspnea

-- Supportive: acetaminophen PRN, incentive spirometry, benzonatate, dextromethorphan

Red Flags

  • CURB-65 ≥3 or 1 major ATS/IDSA severity criterion → ICU admission consideration

  • SpO2 <90% on ≥4L NC or increasing O2 requirement → high-flow nasal cannula (HFNC) or BiPAP; early ICU transfer

  • Septic shock (MAP <65 despite 30 mL/kg IVF) → vasopressors; ICU; blood cultures + antibiotics within 1 hour

  • Cavitary pneumonia + risk factors → S. aureus/MRSA or anaerobic abscess — add vancomycin + metronidazole; thoracic surgery consult

  • Legionella in hospitalized patient → single-source outbreak consideration; public health notification if cluster

  • No improvement at 48–72h on antibiotics → repeat CXR; consider resistant organism, unusual pathogen, or non-infectious etiology

Senior IM Resident Pearls

  • PSI/PORT score is more discriminating than CURB-65 for low-risk patients — PSI class I–II can safely be treated outpatient; CURB-65 simpler for quick bedside use

  • 5-day CAP therapy is guideline-supported (IDSA/ATS 2019) when clinical stability criteria met — longer courses do not improve outcomes and increase resistance

  • MRSA nares swab negative = ~98% NPV for MRSA pneumonia — powerful de-escalation tool at 48h when initial culture results pending

  • Legionella urine antigen detects serogroup 1 only (~85% of cases) — negative antigen does NOT rule out Legionella; cover with macrolide or fluoroquinolone in severe CAP regardless

  • Recurrent pneumonia in the same lobe → post-obstructive pneumonia from endobronchial obstruction → CT chest and bronchoscopy to rule out malignancy

  • Common mistake: Starting antibiotics before blood cultures in CAP — cultures are positive in ~10% and the only way to narrow therapy; draw cultures before first dose whenever possible

  • Common mistake: Treating viral CAP with antibiotics — low procalcitonin (<0.1 ng/mL) + viral panel positive + no bacterial features = antibiotic-sparing approach appropriate

Note
For inpatient CAP, start with CTX + Azithro or Doxy (β-lactam + macrolide; doxy can substitute for macrolide); If unable to take β-lactam + macrolide, use a respiratory FQ such as levofloxacin or moxifloxacin. Add Vanc (per pharm) or Linezolid if MRSA risk (Hx MRSA, recent flu, immunosuppression, IVDU, IV abx in past 3 mo). If Pseudomonas risk (prior Pseudomonas infx, GNR on stain, IV abx in past 3 mo, chronic COPD on steroids), use Cefepime + Levo (or moxi). If risk for both MRSA + Pseudomonas, use Cefepime + Levo/Moxi + Vanc (or Linezolid). For HAP, treat with Cefepime + Vanc. Treat CAP for ≥5 days once clinically stable; uncomplicated MRSA ~7 days; MRSA with bacteremia ≥14 days; Pseudomonas or unusual pathogens 7–14 days (longer if complications). Avoid cephalosporins/carbapenems in severe β-lactam allergy. QT risk is the main concern with macrolides/FQs. Common doses: CTX 1–2 g IV daily; Azithro 500 mg IV/PO daily x 3 ; Doxy 100 mg BID; Levo 750 mg IV/PO daily; Moxi 400 mg IV/PO daily; Cefepime 2 g IV q8h; Cipro 400 mg IV q8h; Linezolid 600 mg IV q12h; Vanc per pharmacy dosing.

Labs

  • CBC daily

  • BMP/RFP daily

  • Mg daily

  • LFTs

  • Procalcitonin

  • Blood cultures x2 (before antibiotics)

  • Sputum Gram stain & culture

  • Legionella urine antigen

  • Pneumococcal urine antigen

  • Viral respiratory panel (COVID/Flu/RSV)

  • ABG/VBG if hypoxic or significant respiratory distress

  • HIV test if risk factors or atypical presentation

  • MRSA nares if severe pneumonia

  • Trend fever curve

Imaging

  • CXR

  • CT Chest w/ contrast if:

    • No improvement after 48–72 hrs

    • Recurrent pneumonia

    • Concern for obstruction/malignancy

    • CXR nondiagnostic

  • Ultrasound chest if pleural effusion suspected

Antibiotics

Standard CAP

  • Ceftriaxone 2 g IV q24h × 5 days

  • Azithromycin 500 mg IV/PO daily × 3 days

Aspiration Concern

  • Ampicillin-Sulbactam (Unasyn) 3 g IV q6h

  • Azithromycin 500 mg daily

Severe CAP

  • Cefepime 2 g IV q8h

  • Vancomycin (pharmacy dosing)

  • Azithromycin 500 mg daily

HAP

  • Cefepime 2 g IV q8h

  • Vancomycin (pharmacy dosing)

Supportive Medications

  • Acetaminophen 650 mg PO q6h PRN fever/pain

  • Benzonatate 100–200 mg PO TID PRN cough

  • Dextromethorphan PRN cough

  • Supplemental oxygen PRN

Steroids (only selected patients)

If severe CAP/shock:

  • Hydrocortisone 50 mg IV q6h

OR

  • Prednisone 50 mg PO daily × 4–7 days

Monitoring

  • Telemetry (if severe illness)

  • Continuous pulse ox

  • Vital signs q4h

  • Strict I&O

  • Daily weights

  • Daily CBC/RFP

  • Monitor oxygen requirements

Consults

  • PT/OT eval and treat

  • Respiratory Therapy

  • Infectious Disease (refractory/complex cases)

  • Pulmonology if:

    • Recurrent pneumonia

    • Large effusion

    • Concern for bronchoscopy

  • Interventional Radiology/Pulm for thoracentesis if indicated

Nursing

  • Incentive spirometry q1h while awake

  • Pulmonary hygiene

  • Early ambulation

  • Aspiration precautions if indicated

  • Fall precautions

DVT PPX

  • Enoxaparin 40 mg SQ daily

OR

  • Heparin 5000 units SQ q8h

Diet

  • Regular diet

  • Cardiac diet if indicated

  • Aspiration precautions/dysphagia diet if needed

Follow-up Cultures

  • Follow blood cultures

  • Follow sputum cultures

  • Follow urine antigens

  • Follow viral panel

  • Narrow antibiotics when data available

Source Control

  • Evaluate pleural effusion

  • Thoracentesis if:

    • Effusion >10 mm

    • Large parapneumonic effusion

    • Suspected empyema

    • Symptomatic dyspnea

Discharge Checklist

  • Afebrile ≥48 hrs

  • Stable oxygen requirement

  • Clinically improving

  • Transition to PO antibiotics:

    • Amoxicillin 875 mg PO BID (typical CAP)

    • Levofloxacin 750 mg PO daily (selected cases)

    • Linezolid 600 mg PO BID (MRSA)

  • PCP follow-up within 1 week

  • Repeat imaging in 6–8 weeks for:

    • Smokers

    • Recurrent pneumonia

    • Persistent symptoms

  • MRSA risk factors include recent influenza or viral illness, prior MRSA infection or colonization, IV drug use, skin/soft tissue infections (pustules/abscess), cavitary pneumonia, recent hospitalization (especially with IV antibiotics), and a positive MRSA nasal swab.

  • Pseudomonas risk factors include COPD (especially severe or with frequent exacerbations), bronchiectasis, structural lung disease, prior Pseudomonas colonization/infection, recent hospitalization with IV antibiotics, immunosuppression, chronic steroid use, and nursing home or healthcare exposure.

  • Aspiration risk factors include dementia or altered mental status, alcohol or drug use, dysphagia (e.g., stroke), GERD, poor dentition, seizure, impaired gag reflex, and being bedridden.

Notes:

  • Streptococcus pneumoniae (most common bacterial CAP pathogen)

  • in those with comorbidities, older age, or recent antibiotic -> also we cover for Beta-lactamase-producing Haemophilus influenzae, Moraxella catarrhalis_Methicillin-susceptible _Staphylococcus aureus