Meningitis

complete reference · LP/CSF interpretation · empiric antibiotics + dexamethasone · Listeria coverage · Full Card

Symptoms / Associated Sx

• Classic triad of fever, headache, and nuchal rigidity, often with photophobia and altered mental status — but all three triad elements are present in fewer than half of patients; nearly all have at least two of fever/headache/stiff neck/altered mentation. Bacterial: rapid onset, toxic appearance, may have a petechial/purpuric rash (meningococcemia). Viral: generally milder with preserved mentation. Kernig and Brudzinski signs are specific but insensitive. Seizures or focal deficits raise concern for complications or encephalitis.

Neg

• No instantaneous thunderclap onset — argues against SAH (though SAH can cause meningismus from chemical irritation; CT/LP/xanthochromia distinguish)

• Mentation preserved and patient non-toxic — favors viral/aseptic over bacterial (prominent altered mental status, seizures, or focal signs point to bacterial meningitis or encephalitis)

• No focal deficit, papilledema, or immunocompromise mandating pre-LP imaging — supports proceeding directly to LP (those features require CT first to exclude a mass/raised ICP)

• No prominent personality/behavioral change or temporal-lobe seizures — argues against HSV encephalitis as the dominant process (overlap exists; cover with acyclovir if uncertain)

Social History (SHx)

• Sick contacts, crowded living (dormitory, military barracks — meningococcus); vaccination history (pneumococcal, meningococcal, Hib); recent upper-respiratory or ear/sinus infection.

• Immunocompromise (HIV, transplant, steroids, asplenia, complement deficiency), pregnancy, age extremes; recent neurosurgery, head trauma, or CSF leak (nosocomial organisms); injection drug use.

Main Etiology

• Bacterial: Streptococcus pneumoniae (most common in adults), Neisseria meningitidis (young adults, outbreaks, rash), Listeria monocytogenes (age >50, immunocompromised, pregnant, neonates), Haemophilus influenzae; group B Strep and E. coli in neonates; staph/gram-negatives post-neurosurgery.

• Viral (aseptic): enteroviruses (most common), HSV, VZV, arboviruses, HIV (seroconversion). Other: Cryptococcus (HIV/immunocompromised), tuberculous meningitis, fungal; non-infectious (drug-induced, carcinomatous/leptomeningeal).

RF

• Modifiable: incomplete vaccination, crowded living conditions, untreated parameningeal infection (otitis/sinusitis).

• Non-modifiable: age extremes, immunocompromise/HIV, asplenia, complement deficiency (recurrent meningococcus), anatomic CSF leak/dural defect.

Data

• Lumbar puncture — opening pressure, cell count with differential, glucose, protein, Gram stain and culture; add PCR (enterovirus, HSV, VZV; multiplex meningitis/encephalitis panel), cryptococcal antigen and AFB/TB studies in the right host.

• CSF patterns:

  TypeCellsGlucoseProtein Bacterial↑↑ neutrophils (100s–1000s)lowhigh Viral↑ lymphocytesnormalnormal/mild↑ Fungal/TB↑ lymphocyteslowhigh

• Two sets of blood cultures before antibiotics; CBC, CMP, lactate, coagulation studies, HIV test; procalcitonin/CRP as adjuncts.

• CT head before LP only if focal neurologic deficit, papilledema, depressed/declining consciousness, new seizure, immunocompromised, or age >60 (raised-ICP/mass risk) — otherwise LP without prior imaging. If imaging is required, draw cultures and give dexamethasone + antibiotics first, then image, then LP.

DDx

Subarachnoid hemorrhage (thunderclap, blood/xanthochromia on LP) · encephalitis (prominent altered mentation, seizures, focal/temporal signs — HSV) · brain abscess (focal deficit, ring-enhancing lesion, do not LP) · viral vs bacterial meningitis (CSF profile) · drug-induced aseptic meningitis (NSAIDs, TMP-SMX, IVIG) · leptomeningeal carcinomatosis (malignancy, cytology)

Home Meds

• Continue essential home medications; there are no specific holds — the priority is rapid administration of antimicrobials.

• Reconcile drugs that can cause aseptic meningitis (NSAIDs, TMP-SMX, IVIG) if the picture is aseptic and recurrent.

Plan

Consults

• Infectious disease — pathogen-directed therapy and duration.

• Neurology — encephalitis overlap, seizures, complications.

• Neurosurgery — hydrocephalus, abscess, or a CSF-leak/shunt source.

• ICU — septic shock, depressed consciousness, status epilepticus, or raised ICP.

Timing — do not delay antimicrobials

• Antibiotics within the first hour; never delay for the LP or CT. Sequence when imaging is required: draw blood cultures → give dexamethasone + empiric antibiotics → obtain CT → then LP (CSF chemistry/PCR remain useful even after a dose or two of antibiotics).

Adjunctive steroids

• Dexamethasone (Decadron) 10 mg IV q6h for 4 days — give before or with the first antibiotic dose in suspected bacterial meningitis (reduces mortality and neurologic sequelae, especially hearing loss, in pneumococcal disease). Discontinue if cultures show a non-pneumococcal organism.

Empiric antimicrobials

• Standard adult: ceftriaxone (Rocephin) 2 g IV q12h + vancomycin (Vancocin) 15–20 mg/kg IV q8–12h (target trough/AUC; covers resistant pneumococcus).

• Add ampicillin 2 g IV q4h if age >50, immunocompromised, pregnant, or alcoholic (Listeria coverage — cephalosporins miss it).

• Add acyclovir (Zovirax) 10 mg/kg IV q8h if any encephalitis features (altered mentation, seizures, focal/temporal signs) until HSV is excluded.

• Post-neurosurgical/penetrating trauma: vancomycin + cefepime or meropenem (cover staph and Pseudomonas). Adjust all for renal function.

De-escalation / viral

• Narrow therapy to culture/PCR results with ID guidance; typical durations ~7 days (meningococcus/H. flu), 10–14 days (pneumococcus), ≥21 days (Listeria). Viral/aseptic meningitis (enterovirus) is usually self-limited and supportive; treat HSV with acyclovir.

Public health / isolation

• Droplet precautions for suspected meningococcal disease until 24h of effective therapy; arrange post-exposure prophylaxis for close contacts (rifampin, ciprofloxacin, or ceftriaxone); report notifiable infections to public health.

Always

• PT / OT eval and treat — assess for neurologic sequelae; audiology evaluation (sensorineural hearing loss, especially pneumococcal).

• Trend: mental status, fever curve, hemodynamics, serial neuro exams; CSF results to refine therapy; repeat imaging if focal signs/hydrocephalus develop.

• Escalation triggers: septic shock → ICU and resuscitation · GCS decline or signs of raised ICP/herniation → ICU, neurosurgery · status epilepticus → ICU · acute hydrocephalus → EVD.

• Discharge checklist: complete the pathogen-specific antibiotic course (often via OPAT) · audiology follow-up · vaccination of unimmunized/asplenic patients · contact prophylaxis confirmed and public-health reporting done · neurology follow-up for any deficits/seizures · evaluate for a predisposing source (CSF leak, sinus/ear focus, immunodeficiency if recurrent) · return precautions.

Red Flags — ICU / Urgent

• Purpuric/petechial rash + hypotension (meningococcemia/Waterhouse-Friderichsen) → ICU, immediate antibiotics.
• Depressed or declining consciousness, signs of raised ICP → ICU; do not LP before imaging.
• Septic shock → resuscitation, vasopressors, ICU.
• Status epilepticus or focal deficits → consider encephalitis/complication; cover HSV, ICU.
• Acute hydrocephalus → neurosurgery for EVD.

Senior IM Resident Pearls

• Antibiotics first, imaging second, LP when safe. The single biggest mistake is delaying antimicrobials to "complete the workup." Blood cultures, then dexamethasone + antibiotics, then CT/LP if imaging is indicated.
• Dexamethasone goes before or with the first antibiotic dose — its mortality and hearing-loss benefit in pneumococcal meningitis is lost if given after. Stop it once you know it isn't pneumococcus.
• Don't forget Listeria. Ceftriaxone + vancomycin misses it — add ampicillin in anyone >50, immunocompromised, or pregnant. This is a classic boards and ward miss.
• If it could be encephalitis, add acyclovir. Untreated HSV encephalitis is devastating; empiric acyclovir while awaiting PCR is low-risk and high-yield.
• You don't need a CT before every LP. Image first only with focal deficit, papilledema, depressed consciousness, seizure, immunocompromise, or age >60 — routine pre-LP CT just delays treatment.
• The CSF tells the story: neutrophils + low glucose + high protein = bacterial; lymphocytes + normal glucose = viral; lymphocytes + low glucose = TB/fungal.
• Treat the contacts and call public health for meningococcus — droplet isolation for 24h and prophylaxis for close contacts.
• Common mistake: attributing a partially-treated, lymphocyte-predominant CSF to "viral" when prior oral antibiotics blunted a bacterial picture — correlate with clinical severity and PCR, and don't under-treat.