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Bacterial meningitis in adults
When bacterial meningitis is suspected, take blood cultures and start dexamethasone and antibiotics at once; if a CT is needed before lumbar puncture, treatment comes first and does not wait for the scan.
Why it matters in the exam
The question presents an adult with fever, headache, neck stiffness and altered consciousness, sometimes with a petechial rash (Meningococcus). The candidate must order the steps: blood cultures, then lumbar puncture — unless there is an indication for CT first (immunosuppression, new seizure, papilloedema, focal neurological deficit or a marked fall in consciousness). In that case dexamethasone and antibiotics are given before the CT. Empirical antibiotics in an adult: ceftriaxone 2 g every 12 hours with vancomycin where resistant pneumococcus occurs, and over age 50, in immunosuppression, pregnancy and alcohol use disorder, ampicillin is added to cover Listeria.
Spinal fluid interpretation is almost always tested: bacterial — many neutrophils, low glucose (ratio to blood glucose below 0.4) and high protein; viral — lymphocytes and normal glucose; tuberculous — lymphocytes, low glucose and very high protein. Dexamethasone 10 mg every 6 hours for 4 days, started just ahead of the antibiotics or alongside them, cuts deaths and nerve damage, above all in pneumococcal infection. Meningococcus needs droplet isolation for 24 hours and prophylaxis for close contacts (single-dose ciprofloxacin, rifampicin or ceftriaxone). With confusion, fever and temporal lobe changes, think of HSV encephalitis and add acyclovir.
Key points
- Blood cultures, then lumbar puncture; CT first only when indicated.
- Ceftriaxone 2 g every 12 hours + vancomycin; + ampicillin over 50.
- Dexamethasone 10 mg every 6 hours for 4 days, before or with the antibiotics.
- Bacterial fluid: neutrophils, low glucose (ratio below 0.4), high protein.
- Meningococcus: isolation for 24 hours and prophylaxis for contacts.
Summary table
| Topic | Finding / indication | Action | Exam note |
|---|---|---|---|
| Bacterial fluid | Neutrophils, low glucose (ratio below 0.4), high protein | Full empirical treatment | Gram stain and culture |
| Viral fluid | Lymphocytes, normal glucose | Supportive; acyclovir if HSV suspected | PCR for enterovirus and HSV |
| Tuberculous fluid | Lymphocytes, low glucose, very high protein | Antituberculous treatment + steroids | Gradual onset |
| CT before puncture | Immunosuppression, seizure, papilloedema, focal deficit, falling consciousness | Antibiotics and dexamethasone before the CT | Never delay treatment |
| Empirical treatment | Every adult | Ceftriaxone 2 g every 12 hours + vancomycin | + ampicillin over 50, immunosuppressed, pregnant |
| Dexamethasone | Before or with the first dose | 10 mg every 6 hours for 4 days | Main benefit in pneumococcal disease |
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Sources
- ESCMID Guideline: Diagnosis and Treatment of Acute Bacterial Meningitis, 2016 — Imaging before lumbar puncture, dexamethasone and empirical antibiotics
- Harrison's Principles of Internal Medicine, 21st edition (2022) — Acute Meningitis
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-02. The text may contain errors; when in doubt, check the source.