bacterial meningitis
Contents
Medical emergency — antibiotics within 60 minutes, ideally within 30. Empiric: ceftriaxone + vancomycin ± ampicillin (if age ≥50 or immunocompromised for Listeria cover). Dexamethasone before or with the first antibiotic dose — proven mortality benefit for pneumococcal meningitis (European Dexamethasone Study (2002)). LP before antibiotics only if it will not delay treatment; CT before LP only if specific indications present.
- dexamethasone 0.15 mg/kg IV q6h × 4 days — give BEFORE or WITH first antibiotic dose (not after)
- first-line: ceftriaxone 2 g IV q12h + vancomycin 15–20 mg/kg IV q8–12h (target trough 15–20 mg/L)
- if age ≥50 or immunocompromised: ADD ampicillin 2 g IV q4h (Listeria cover)
- if severe penicillin/cephalosporin allergy: meropenem 2 g IV q8h + vancomycin (or chloramphenicol if carbapenem allergy — rare)
- LP before antibiotics ONLY if no delay — blood cultures then antibiotics immediately if LP will be delayed
- CT before LP only if: focal neuro deficit, altered consciousness, papilloedema, seizures, immunocompromised
- tailor therapy to CSF culture + susceptibilities within 48–72 h
Penicillin-resistant S. pneumoniae prevalence guides the need for empiric vancomycin. In most Canadian centres, resistance rates warrant routine vancomycin until susceptibilities return.
when to suspect
Classic triad (fever + neck stiffness + altered mental status) present in <50% — maintain high index of suspicion.
- acute fever + headache + any of: neck stiffness, photophobia, altered consciousness, petechial/purpuric rash (meningococcal)
- Kernig and Brudzinski signs: low sensitivity (~5%), reasonable specificity — absence does not rule out meningitis
- jolt accentuation test: worsening headache with rapid horizontal head rotation — more sensitive than Kernig/Brudzinski
CT before LP — indications
LP can proceed without CT in most patients. CT first only if:
- focal neurological deficit
- new-onset seizures
- papilloedema
- altered level of consciousness (GCS <12)
- immunocompromised (HIV, transplant, immunosuppressive therapy)
- history of CNS disease (mass, stroke, focal infection)
If CT is indicated before LP → draw blood cultures → give empiric antibiotics + dexamethasone immediately → then CT → then LP. Antibiotics do not significantly reduce CSF culture yield within the first 1–2 hours.
CSF interpretation
| parameter | bacterial | viral | TB |
|---|---|---|---|
| opening pressure | ↑↑ (>30 cm H₂O) | normal–↑ | ↑↑ |
| WBC | >1000 × 10⁶/L (neutrophilic) | 10–500 (lymphocytic) | 100–500 (lymphocytic) |
| protein | ↑↑ (>1.0 g/L) | normal–↑ | ↑↑ |
| glucose | ↓↓ (CSF:serum <0.4) | normal | ↓↓ |
| gram stain | positive in 60–90% | negative | AFB rarely positive |
Send: cell count + differential, protein, glucose (with paired serum glucose), gram stain, culture, and consider multiplex PCR panel if available.
empiric therapy — detail
by age and risk group
| patient group | likely organisms | empiric regimen |
|---|---|---|
| 18–49, immunocompetent | S. pneumoniae, N. meningitidis | ceftriaxone 2 g IV q12h + vancomycin |
| ≥50 or immunocompromised | above + Listeria monocytogenes | ceftriaxone + vancomycin + ampicillin 2 g IV q4h |
| post-neurosurgical / VP shunt | S. aureus, S. epidermidis, gram-negatives | vancomycin + cefepime 2 g IV q8h (or meropenem) |
| basilar skull fracture | S. pneumoniae, H. influenzae, GAS | ceftriaxone + vancomycin |
penicillin allergy
| allergy history | approach |
|---|---|
| non-anaphylactic | ceftriaxone safe (<2% cross-reactivity) |
| confirmed anaphylaxis to all β-lactams | meropenem 2 g IV q8h (higher dose for CNS penetration) + vancomycin |
| if Listeria cover needed + β-lactam allergy | TMP-SMX 5 mg/kg IV q6h (alternative to ampicillin for Listeria) |
dexamethasone
European Dexamethasone Study (2002): dexamethasone 0.15 mg/kg IV q6h × 4 days reduced mortality and unfavourable outcomes in pneumococcal meningitis. Benefit not demonstrated for other organisms, but guideline recommendation is to give empirically (before pathogen known) and discontinue if non-pneumococcal.
- give before or with first antibiotic dose — no benefit if given >1 h after antibiotics
- continue × 4 days if S. pneumoniae confirmed
- discontinue if another pathogen identified (or if meningitis ruled out)
- may reduce vancomycin CSF penetration — monitor closely; some centres use rifampicin as adjunct
targeted therapy once pathogen known
| organism | preferred | duration |
|---|---|---|
| S. pneumoniae (penicillin-susceptible) | ceftriaxone 2 g IV q12h (or penicillin G 4 MU IV q4h) | 10–14 days |
| S. pneumoniae (penicillin-resistant) | ceftriaxone + vancomycin | 10–14 days |
| N. meningitidis | ceftriaxone 2 g IV q12h (or penicillin G) | 7 days |
| L. monocytogenes | ampicillin 2 g IV q4h ± gentamicin | 21 days |
| H. influenzae | ceftriaxone 2 g IV q12h | 7 days |
| GBS | ampicillin or penicillin G | 14–21 days |
post-exposure prophylaxis
meningococcal contacts
- close contacts (household, kissing, shared utensils, healthcare workers performing mouth-to-mouth): ciprofloxacin 500 mg PO single dose (adults) or rifampicin 600 mg PO q12h × 2 days or ceftriaxone 250 mg IM single dose
- notify public health immediately
traps
- do not delay antibiotics for LP or CT — mortality increases with each hour of delay
- a normal CT does not exclude elevated ICP — if clinical concern remains, proceed with caution or defer LP
- partially treated meningitis (e.g. oral antibiotics given in the community before presentation): CSF may show lymphocytic pleocytosis, lower protein, and negative cultures — mimics viral meningitis; send PCR and treat empirically
- Listeria is intrinsically resistant to cephalosporins — ceftriaxone alone does not cover Listeria; must add ampicillin in at-risk patients
- meningococcal disease can present as isolated septicaemia without meningitis — purpuric rash + shock without meningismus still warrants meningococcal-dose ceftriaxone
- dexamethasone given after antibiotics provides no benefit — timing is everything