Meningitis and Encephalitis

Meet the patient

A 19-year-old university student reaches the emergency department after twelve hours of fever, headache and vomiting, now drowsy. A rapidly spreading non-blanching purpuric rash covers his buttocks and ankles. GCS is 13, temperature 39.6 degrees C. NICE treats a haemorrhagic non-blanching rash with lesions larger than 2 mm as a red flag for meningococcal disease; the rash may be absent, and that does not exclude the diagnosis.^[2]

Two questions govern the next hour: which antibiotic goes in now, and does anyone wait for a scan? The first dose is not delayed for CT or LP if either would cause a clinically significant delay.^[2][8]

Two diseases, one emergency

Meningitis is inflammation of the meninges; encephalitis is inflammation of the brain parenchyma, and the two blur as meningoencephalitis. The split that changes therapy is bacterial meningitis (time-critical antibiotics and dexamethasone) versus HSV encephalitis (time-critical aciclovir when the syndrome is strongly suspected). NICE does not routinely add aciclovir to bacterial-meningitis treatment unless herpes simplex encephalitis is strongly suspected.^[2][1]

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Epidemiology — what actually grew in a nationwide adult cohort

In the Dutch MeninGene cohort (2974 adults, 2006–2024), S. pneumoniae caused 68 per cent, N. meningitidis 11 per cent, L. monocytogenes 6 per cent, H. influenzae 4 per cent, and S. pyogenes 3 per cent. Overall mortality was 17 per cent and stable over 18 years. Listeria had the highest mortality at 32 per cent, then pyogenes 19 per cent and pneumococcus 18 per cent. An unfavourable outcome occurred in 39 per cent. Among survivors, neurological sequelae occurred in 55 per cent, including hearing impairment in 31 per cent and cognitive impairment in 23 per cent. Absence of adjunctive dexamethasone was a key predictor of unfavourable outcome.^[9]

The older 1998–2002 Dutch cohort (696 episodes) had pneumococcus in 51 per cent and meningococcus in 37 per cent, overall mortality 21 per cent, and an unfavourable outcome in 34 per cent — the organism mix has shifted toward pneumococcus as meningococcus declined.^[1]

Listeria meningitis patients were more often immunocompromised (66 per cent vs 28 per cent). In 22 per cent of Listeria cases, amoxicillin was not given on the first day of admission — a missed cover that the NICE add-on rule is designed to prevent.^[9][2]

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The clinical picture — the triad is fever, neck stiffness and altered mental status

The classic triad is fever, neck stiffness and a change in mental status, not fever–headache–neck stiffness. It was present in only 44 per cent of the 2004 cohort and 39 per cent of the 2006–2024 cohort. In 2004, 95 per cent had at least two of four symptoms: headache, fever, neck stiffness, and altered mental status. On admission, 14 per cent were comatose and 33 per cent had focal neurologic abnormalities. NICE names fever, headache, neck stiffness and altered consciousness or cognition as the red-flag combination.^[1][9][2]

A haemorrhagic non-blanching rash with lesions larger than 2 mm (purpura), a rapidly spreading petechial or purpuric rash, or any meningitis features combined with a non-blanching rash, strongly suggests meningococcal disease. Do not rule it out because there is no rash.^[2]

^{[1] [2] [5] [1] [2] [4] [7] [9] [10]}

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The first hour — cultures, then the antibiotic, within 60 minutes

NICE: a senior decision-maker ensures antibiotics start within 1 hour of arrival, and that blood tests and lumbar puncture are performed before antibiotics if it is safe and will not cause a clinically significant delay. If the LP will delay the drug, the drug goes first and the LP follows as soon as it is safe.^[2]

In ICU pneumococcal meningitis, Auburtin found that an interval greater than 3 hours from hospital arrival to antibiotics independently predicted 3-month death (OR 14.12), as did a penicillin-nonsusceptible strain (OR 6.83). Three-month mortality was 33 per cent, and 34 per cent of survivors had neurologic sequelae. That is the sourced delay signal — not an unsourced “2-hour doubling.”^[8]

Blood cultures were positive in 76 per cent of the Dutch cohort (1964 of 2572), not “about half.”^[9]

^{[2] [5] [8] [9] [10]}

Dexamethasone — before or with the first dose; still give it if delayed under 12 hours

de Gans (301 adults): dexamethasone 10 mg 15 to 20 minutes before or with the first antibiotic, then every 6 hours for four days. Unfavourable-outcome RR 0.59; mortality RR 0.48. In pneumococcal meningitis, unfavourable outcomes were 26 per cent vs 52 per cent. Gastrointestinal bleeding was not increased (2 vs 5 patients).^[5]

The 2015 Cochrane review (25 trials, 4121 participants) found a non-significant overall mortality reduction (17.8 per cent vs 19.9 per cent, RR 0.90). Steroids did reduce mortality in pneumococcal meningitis (RR 0.84) but not in H. influenzae or N. meningitidis meningitis. Severe hearing loss in children fell with Hib meningitis (RR 0.34), not with non-Haemophilus species. The authors’ conclusion: corticosteroids reduced hearing loss and neurological sequelae but did not reduce overall mortality; data support use in high-income countries.^[3]

NICE operationalises this: give IV dexamethasone for people over 3 months with strongly suspected or confirmed bacterial meningitis; continue it if the organism is pneumococcus or Hib; stop it for all other organisms. Give the first dose with or before the first antibiotic if possible, but do not delay antibiotics to wait for the steroid. If dexamethasone is delayed less than 12 hours after antibiotics, still give it. For meningococcal disease, do not routinely give corticosteroids; consider low-dose replacement corticosteroids in meningococcal septic shock not responding to high-dose vasoactive agents.^[2]

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When to image before the LP — Hasbun features and NICE stops

Hasbun (301 adults with suspected meningitis; 235 scanned): features associated with an abnormal CT were age at least 60 years, immunocompromise, history of CNS disease, seizure within one week, plus neurologic abnormalities (abnormal consciousness, inability to answer two consecutive questions or follow two consecutive commands, gaze palsy, abnormal visual fields, facial palsy, arm or leg drift, abnormal language). When none of those features were present, NPV for a normal CT was 97 per cent.^[6]

NICE imaging-before-LP stops (do not LP until resolved): risk factors for an evolving space-occupying lesion, new focal neurological features (including seizures or posturing), abnormal pupillary reactions, or a GCS of 9 or less (or a progressive, sustained or rapid fall in consciousness). Take bloods, give antibiotics and stabilise before imaging. Do not LP if there is extensive or rapidly spreading purpura, infection at the LP site, or those raised-ICP features.^[2]

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CSF — what the Dutch cohort actually measured

Measure blood glucose immediately before LP so the CSF-to-blood glucose ratio can be calculated. NICE asks for cell count and type, protein, glucose, Gram stain, culture and PCR, with cell counts, protein and glucose available within 4 hours.^[2]

In the Dutch adult cohort the CSF medians were leukocytes 2400/mm3 (IQR 587–6891), protein 3.90 g/L (IQR 2.30–6.10), and glucose 0.50 mmol/L (IQR 0.10–2.50). Blood cultures were positive in 76 per cent. Those are cohort medians for proven bacterial meningitis, not a universal “1000–5000 neutrophils / ratio below 0.4” table.^[9]

Organism-directed duration — NICE stop-rules

Once the organism is known, NICE stop-rules (stop if the person has recovered, otherwise infection-specialist advice): pneumococcus — after 10 days; Hib — after 7 days, continue to 10 if not recovered; meningococcus — after 5 days (the same 5-day stop for meningococcal disease treated as IMD); Listeria — IV amoxicillin or ampicillin for 21 days, with infection-specialist advice on adding co-trimoxazole for the first 7 days; group B strep — after 14 days; Enterobacterales — after 21 days.^[2]

If CSF suggests bacterial meningitis but blood culture and PCR are negative, continue antibiotics for 10 days and stop if recovered.^[2]

HSV encephalitis — trial doses, not an unsourced 14–21-day course

Whitley (biopsy-proven HSV, n = 69 of 208 biopsied): acyclovir 30 mg per kilogram per day versus vidarabine 15 mg/kg/day, for 10 days. Mortality 28 per cent vs 54 per cent. Normal function at six months 38 per cent vs 14 per cent.^[4]

Skoldenberg (Swedish randomised study): acyclovir 10 mg/kg, 8-hourly versus vidarabine 15 mg/kg daily, for 10 days. Mortality 19 per cent vs 50 per cent. At 12 months, no or mild sequelae in 56 per cent vs 13 per cent.^[7]

Those two trials are 10-day regimens. An unsourced “14–21 days, and a 10-day course relapses” claim is not in these abstracts and is not taught here. NICE: do not routinely give IV aciclovir unless HSV encephalitis is strongly suspected.^[2][4][7]

^[4]

Chemoprophylaxis — UKHSA, not an unsourced rifampicin-first script

UKHSA (December 2025): ciprofloxacin is the recommended chemoprophylaxis of choice; rifampicin is the alternative if ciprofloxacin is contraindicated, unavailable, or the strain is (likely) ciprofloxacin-resistant. Adult and 12-and-over ciprofloxacin dose: 500 mg stat. Rifampicin, all ages: twice daily for 2 days; adults and 12-and-over 600 mg. A single IM ceftriaxone dose (125 mg under 12 years, 250 mg 12 and over) is a considered alternative if rifampicin cannot be offered. Cases already treated with IV/IM cephalosporins (ceftriaxone, cefotaxime) do not need carriage-eradicating chemoprophylaxis; penicillin-only cases do.^[10]

Other meningitides (named, not dosed from memory)

TB meningitis, cryptococcal meningitis and autoimmune encephalitis are real differentials (chronic course, HIV, psychiatric prodrome). Load-bearing doses, PCR performance figures and textbook CSF tables for those entities were not fetched in this twin pass and are not taught here. Keep bacterial meningitis and HSV as the two time-critical treatable emergencies sourced above.^[2][4]

Prognosis and disposition

Contemporary adult community-acquired bacterial meningitis still kills 17 per cent, with 39 per cent unfavourable outcomes and neurological sequelae in 55 per cent of survivors. Listeria mortality is 32 per cent. Auburtin’s ICU pneumococcal series: 33 per cent dead at 3 months.^[9][8]

Exam pearls

• Classic triad = fever + neck stiffness + altered mental status — 39–44 per cent; 95 per cent have at least two of four (headache, fever, neck stiffness, AMS).
• Antibiotics within 1 hour of arrival. LP before antibiotics only if safe and not delay-causing. Bloods, antibiotics, stabilise — then image.
• Ceftriaxone: NICE highest BNF/BNFC dose; UKHSA adult suspected-IMD pre-hospital dose 2 g IV/IM stat.
• Dexamethasone 10 mg IV 6-hourly for 4 days, before or with the first antibiotic; still give if delayed less than 12 hours. Continue only for pneumococcus or Hib. Do not routinely steroid meningococcal disease.
• Add IV amoxicillin when Listeria risk factors are present; confirmed Listeria: amoxicillin or ampicillin for 21 days. Listeria mortality 32 per cent.
• Aciclovir only if HSV encephalitis is strongly suspected: 10 mg/kg 8-hourly for 10 days in the landmark trials (Whitley mortality 28 vs 54 per cent).
• Hasbun: age 60+, immunocompromise, known CNS disease, seizure within a week, and focal neuro findings predict an abnormal CT (NPV 97 per cent if none).
• NICE do-not-LP: spreading purpura, GCS 9 or less, new focal neurology/posturing, abnormal pupils.
• Auburtin: more than 3 hours to antibiotics, OR 14.12 for death in ICU pneumococcal meningitis.
• Contacts: ciprofloxacin 500 mg once (12 years and over) is first-line; rifampicin 600 mg twice daily for 2 days is the alternative.
• Meningococcus duration: NICE stop at 5 days if recovered. Pneumococcus: 10 days if recovered.^{[1][2][3][4][5][6][8][9][10]}

Exam application bank (NEET-PG / INICET)

One-line answer

Bacterial meningitis is a 1-hour antibiotic emergency. The classic triad is fever, neck stiffness and altered mental status (only 39–44 per cent complete). HSV encephalitis is the treatable encephalitis not to miss — aciclovir when the picture is strong, 10 mg/kg 8-hourly for 10 days in the landmark trials.^[1][2][4][7]

Worked stems

Stem — purpuric student, first hourShowHide

Model: Strongly suspected meningococcal disease. Bloods, then ceftriaxone at highest BNF dose within 1 hour (UKHSA adult 2 g stat equivalent). Dexamethasone 10 mg with the first antibiotic if bacterial meningitis is still on the table; NICE does not routinely continue steroids once meningococcus is the disease. Do not LP through spreading purpura. Notify public health; ciprofloxacin 500 mg once for close contacts aged 12+.^[2][10]

Stem — ceftriaxone alone in an immunocompromised 66-year-oldShowHide

Model: NICE requires IV amoxicillin in addition to ceftriaxone or cefotaxime when Listeria risk factors are present. Dutch Listeria cases were immunocompromised in 66 per cent, and 22 per cent did not receive amoxicillin on day 1. Listeria mortality was 32 per cent. Confirmed Listeria: amoxicillin or ampicillin for 21 days.^[2][9]

Stem — fever, seizure, burning-rubber hallucinationShowHide

Model: Strongly suspected HSV encephalitis. Start aciclovir 10 mg/kg IV 8-hourly now (trial course 10 days). Cover bacterial meningitis in parallel until excluded. Seizure within a week is a Hasbun CT-associated feature — antimicrobials first, then image, then LP.^[2][4][6][7]

Red flags

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References10ShowHide

1. [1]van de Beek D, de Gans J, Spanjaard L, Weisfelt M, Reitsma JB, Vermeulen M. Clinical features and prognostic factors in adults with bacterial meningitis. New England Journal of Medicine, 2004.PMID 15509818
2. [2]National Institute for Health and Care Excellence. Meningitis (bacterial) and meningococcal disease: recognition, diagnosis and management NICE guideline NG240, 2024.Source
3. [3]Brouwer MC, McIntyre P, Prasad K, van de Beek D. Corticosteroids for acute bacterial meningitis. Cochrane Database of Systematic Reviews, 2015.PMID 26362566
4. [4]Whitley RJ, Alford CA, Hirsch MS, Schooley RT, Luby JP, Aoki FY, Hanley D, Nahmias AJ, Soong SJ. Vidarabine versus acyclovir therapy in herpes simplex encephalitis. New England Journal of Medicine, 1986.PMID 3001520
5. [5]de Gans J, van de Beek D. Dexamethasone in adults with bacterial meningitis. New England Journal of Medicine, 2002.PMID 12432041
6. [6]Hasbun R, Abrahams J, Jekel J, Quagliarello VJ. Computed tomography of the head before lumbar puncture in adults with suspected meningitis. New England Journal of Medicine, 2001.PMID 11742046
7. [7]Sköldenberg B, Forsgren M. Acyclovir versus vidarabine in herpes simplex encephalitis. Scandinavian Journal of Infectious Diseases Supplementum, 1985.PMID 3912977
8. [8]Auburtin M, Wolff M, Charpentier J, Varon E, Le Tulzo Y, Girault C, Mohammedi I, Renard B, Mourvillier B, Bruneel F, Ricard JD, Timsit JF. Detrimental role of delayed antibiotic administration and penicillin-nonsusceptible strains in adult intensive care unit patients with pneumococcal meningitis. Critical Care Medicine, 2006.PMID 16915106
9. [9]Drost EHGM, Schepers EN, Chekrouni N, van Soest TM, Koelman DLH, Bijlsma MW, Brouwer MC, van de Beek D. Outcomes of adults with community-acquired bacterial meningitis in the Netherlands: a prospective nationwide cohort study. Lancet Regional Health Europe, 2026.PMID 41323877
10. [10]UK Health Security Agency. Guidance for public health management of meningococcal disease in the UK UKHSA, 2025.Source