① CT head before lumbar puncture?
Image first if any of these is present (otherwise proceed straight to LP):
- Age ≥ 60 years
- Immunocompromised state
- History of CNS disease (mass lesion, stroke, focal infection)
- New-onset seizure (within 1 week)
- Papilledema
- Abnormal level of consciousness (unable to follow two consecutive commands; any GCS < 15)
- Focal neurologic deficit (excluding isolated cranial nerve palsy)
Absence of all of the above has ~97% negative predictive value for a normal CT. If LP is delayed for imaging, antibiotics + dexamethasone must still go in within the time target.
② CSF interpretation (typical patterns)
| Bacterial | Viral / aseptic |
|---|
| Opening pressure | ↑ (often > 180–300 mm H₂O) | Normal / mildly ↑ |
| WBC | Typically 1,000–5,000/µL (range <100 to >10,000), neutrophilic | < 250/µL, lymphocytic |
| Glucose (CSF:serum) | Low, < 40 mg/dL (ratio < 0.4) | Normal |
| Protein | High (> 100–200 mg/dL) | Normal / mildly ↑ |
| Gram stain | Positive in ~60–90% | Negative |
No single value rules meningitis in or out — bacterial meningitis can present with only modestly elevated or even near-normal CSF WBC early, when partially treated, or in neutropenia. Send Gram stain, culture, glucose, protein, cell count, and pathogen PCR; pair with 2 sets of blood cultures.
Recent Updates
- The first global WHO 2025 meningitis guidelines recommend IV ceftriaxone or cefotaxime first-line (strong), adding ampicillin/amoxicillin when Listeria risk factors are present (strong), and considering vancomycin where pneumococcal penicillin/cephalosporin resistance is prevalent (conditional; rifampicin is an alternative).
- Dexamethasone should be given before or with the first antibiotic dose; the mortality and disability benefit is greatest in pneumococcal meningitis (de Gans & van de Beek, NEJM 2002).
- A CT head before LP is reserved for specific risk features — routine imaging only delays life-saving antibiotics.
Source: WHO Guidelines on Meningitis Diagnosis, Treatment and Care 2025; van de Beek D, et al. ESCMID 2016; Tunkel AR, et al. IDSA 2004. (See Sources.)
Key Knowledge Points
- Antibiotics and dexamethasone within ~1 hour — never delay for imaging or LP.
- Meningitis requires CNS-penetrating doses, higher and more frequent than usual systemic doses.
- Add ampicillin for Listeria when age ≥ 50, immunocompromised, pregnant, or alcohol use disorder.
- De-escalate to pathogen-directed therapy once Gram stain, culture, and susceptibilities return; stop dexamethasone if not pneumococcal.
About This Tool
This tool supports the first hour of managing an adult with suspected acute bacterial meningitis: deciding whether to image before lumbar puncture, interpreting the CSF, and choosing empiric antibiotics with CNS-penetrating doses plus adjunctive dexamethasone. It distills IDSA, ESCMID, and WHO guidance into one workflow. Empiric therapy is a bridge to pathogen-directed treatment — narrow it as soon as cultures and susceptibilities allow.
How to Use This Tool
- Use the CT-before-LP checklist and start antibiotics + dexamethasone without delay.
- Select the host / clinical setting — this sets Listeria and Gram-negative coverage.
- Flag a severe β-lactam allergy or encephalitis features if present.
- Review the regimen, the CNS doses, dexamethasone, and the always-do steps.
- Adjust every maintenance dose for renal function and monitor vancomycin by AUC.
Frequently Asked Questions (FAQ)
1. Should I delay antibiotics until after the LP or CT?
No. Give antibiotics with dexamethasone within about one hour; do not wait for imaging or LP. If CT is needed first, draw blood cultures and give dexamethasone plus antibiotics before the scan. CSF cultures may still be informative for several hours after the first dose.
2. Who needs a CT head before LP?
Image first for age ≥ 60, immunocompromise, a history of CNS disease, new-onset seizure (within a week), papilledema, abnormal consciousness (inability to follow two consecutive commands; any GCS < 15), or a focal neurologic deficit (excluding isolated cranial nerve palsy). Without these, the chance of an abnormal CT is very low and LP can proceed.
3. When do I add ampicillin?
When there is a risk factor for Listeria monocytogenes: age 50 or older, pregnancy, immunocompromise, or alcohol use disorder. Cephalosporins and vancomycin do not cover Listeria.
4. How is dexamethasone dosed, and when do I stop it?
Dexamethasone 10 mg IV every 6 hours for 4 days, started just before or with the first antibiotic dose. Continue the course if pneumococcus is confirmed or remains the leading suspect (including culture-negative cases); stop it if a non-pneumococcal organism is identified, and generally avoid it in confirmed Listeria. The benefit is established mainly in high-income settings and pneumococcal disease; WHO 2025 advises against routine use during meningococcal epidemics.
5. Why are the doses higher than usual?
The blood-brain barrier limits drug entry, so meningitis needs higher, more frequent dosing (e.g., ceftriaxone 2 g q12h). Give full empiric and loading doses regardless of renal function; adjust maintenance for renal function — usually by extending the interval rather than cutting the dose — and use AUC-guided vancomycin.
Related Tools
📖 Sources:
- Tunkel AR, et al. (2004). Practice guidelines for the management of bacterial meningitis (IDSA). Clin Infect Dis. PMID 15494903.
- Tunkel AR, et al. (2017). 2017 IDSA clinical practice guidelines for healthcare-associated ventriculitis and meningitis. Clin Infect Dis. 64(6):e34–e65. PMID 28203777.
- van de Beek D, et al. (2016). ESCMID guideline: diagnosis and treatment of acute bacterial meningitis. Clin Microbiol Infect. PMID 27062097.
- World Health Organization (2025). WHO guidelines on meningitis diagnosis, treatment and care. Geneva: WHO; 10 April 2025. ISBN 978-92-4-010804-2.
- de Gans J, van de Beek D (2002). Dexamethasone in adults with bacterial meningitis. N Engl J Med. PMID 12432041.
- Hasbun R, et al. (2001). Computed tomography of the head before lumbar puncture in adults with suspected meningitis. N Engl J Med. 345(24):1727–33. PMID 11742046.
- van de Beek D, et al. (2016). Community-acquired bacterial meningitis (review). Nat Rev Dis Primers. 2:16074. PMID 27808261.
- Brouwer MC, et al. (2010). Epidemiology, diagnosis, and antimicrobial treatment of acute bacterial meningitis. Clin Microbiol Rev. 23(3):467–92. PMID 20610819.
- Tunkel AR, et al. (2008). The management of encephalitis: clinical practice guidelines (IDSA). Clin Infect Dis. 47(3):303–27. PMID 18582201.
⚠️ Disclaimer:
This tool is for educational purposes and is not a substitute for professional clinical judgment. Suspected bacterial meningitis is an emergency; management must be individualized by a qualified clinician using the full clinical picture, local resistance data, and specialist input. Doses are CNS (meningitis) doses for normal-renal-function adults and must be adjusted for the individual patient.
