Bacterial meningitis: workup and management
Suspected bacterial meningitis is an emergency: blood cultures, then dexamethasone and empiric antibiotics without delay. Do not hold antibiotics for CT or lumbar puncture. CT before LP only if specific risk features are present.
Working diagnosis
Adult · US guidelines
Draft · awaiting physician review
01Orient
What's new in the evidence
- No major change to US treatment recommendations; dexamethasone with the first antibiotic dose remains standard
- Multiplex CSF PCR panels give rapid results but have false positives and negatives; confirm with culture and stewardship-guided interpretation
- Stop dexamethasone if Listeria is confirmed
Differential diagnoses
- Bacterial meningitis (S. pneumoniae, N. meningitidis, Listeria in >50 or immunocompromised) (can't miss)
- HSV encephalitis (can't miss: add acyclovir)
- Viral (aseptic) meningitis
- Brain abscess, subdural empyema
- Subarachnoid hemorrhage
- Fungal or TB meningitis (immunocompromised)
- Sepsis with delirium from another source
02Assess
Risk scores and decision tools
- CT before LP only with specific risk features (immunocompromise, CNS disease, new seizure, papilledema, abnormal consciousness, focal deficit)
- CSF patterns: bacterial (high neutrophils, low glucose ratio <0.4, high protein)
- Bacterial Meningitis Score (validated in children; not for adults)
Key history questions
- Fever, headache, neck stiffness, confusion, rash
- Recent sinusitis, otitis, head trauma, neurosurgery
- Immunosuppression, asplenia, alcohol use, age >50
- Sick contacts, college dormitory, travel
- Seizures, focal symptoms
- Vaccination history
Examination findings
- Neck stiffness (absence does not exclude)
- Altered mental status, focal deficits, papilledema
- Petechial or purpuric rash (meningococcemia)
- Hemodynamic status
03Investigate
Initial investigations
- Blood cultures ×2 immediately
- CBC, BMP, coagulation, lactate, glucose
- Lumbar puncture: opening pressure, cell count, protein, glucose (with serum glucose), Gram stain, culture, HSV PCR, multiplex PCR
Advanced investigations
- CT head before LP only if: immunocompromised, known CNS disease, new seizure, papilledema, abnormal consciousness or focal deficit
- MRI brain if encephalitis suspected
04Treat
Immediate management
- Dexamethasone 10 mg IV every 6 hours for 4 days, started before or with the first antibiotic dose
- Vancomycin (weight-based, per pharmacy) plus ceftriaxone 2 g IV every 12 hours
- Add ampicillin 2 g IV every 4 hours if age >50, immunocompromised, pregnant or alcohol use disorder (Listeria)
- Add acyclovir 10 mg/kg IV every 8 hours if encephalitis is possible
First-line treatment
- Droplet precautions until meningococcus excluded (24 hours of effective therapy)
- Tailor antibiotics to Gram stain and culture
- Stop dexamethasone if not pneumococcal (unless another indication)
Second-line treatment
- Severe beta-lactam allergy: discuss with ID (e.g., meropenem or alternatives)
- Raised intracranial pressure: ICU, head elevation, osmotherapy
Specialist referrals
- Infectious diseases
- ICU for altered consciousness or shock
- Public health notification for meningococcal disease
05Disposition
Admission criteria
- All suspected bacterial meningitis
Safe discharge criteria
- Not applicable for bacterial meningitis; complete IV course
Follow-up timing
- Audiology testing after recovery; ID follow-up
Patient instructions
- Close contacts of meningococcal cases need chemoprophylaxis
Monitoring
- Neuro checks hourly initially; sodium; hearing
Clinical pearls and pitfalls
- Every hour of antibiotic delay worsens outcome; draw cultures, then treat
- Antibiotics given just before LP reduce culture yield but not cell count changes or PCR
- Chemoprophylaxis for close contacts of meningococcal disease: ciprofloxacin, rifampin or ceftriaxone
RefGuidelines and landmark evidence
For education only. Typical adult starting points; confirm doses against renal function, allergies, interactions and your institution's protocols. Not a substitute for clinical judgment or senior review.