Meningitis and encephalitis
Antibiotics within an hour, before the CT and before the LP if either will cause delay. Add dexamethasone, and aciclovir if the brain itself may be infected.
A 24-year-old student has had a severe headache, fever and vomiting since last night. Light hurts his eyes and his neck is stiff. Now he is confused. There are a few purple spots on his legs that do not fade under a glass. BP 92/60, pulse 126.
Do you wait for the CT and LP before treating?
- Antibiotics within 1 hourCeftriaxone IV. With a non-blanching rash or shock, give it immediately, before anything else.
- Blood cultures first if no delayAnd a throat swab. Never delay antibiotics for them.
- DexamethasoneWith or just before the first antibiotic dose, if bacterial meningitis is suspected.
- Sepsis careOxygen, fluids, lactate, urine output. Call your senior.
- CT first only if neededReduced or falling GCS, focal signs, papilloedema, new fits, or immunosuppression.
- Lumbar punctureWithin 1 hour of arrival if safe. Opening pressure, cell count, protein, glucose (with blood glucose), Gram stain, culture, PCR.
- Encephalitis? Add aciclovirConfusion, behaviour change, fits, focal signs.
- Isolation and public healthDroplet precautions for the first 24 hours of treatment. Notify. Prophylaxis for close contacts.
- Non-blanching rash or shock
- GCS falling or below 13
- Fits
- Focal neurological signs
- Immunosuppressed or pregnant
- Not improving after 24–48 hours
- Meningococcal sepsis
- Herpes simplex encephalitis
- Tuberculous meningitis
- Cerebral malaria
- Subarachnoid haemorrhage
- Brain abscess
| Timing | Antibiotics within 1 hour. Immediately if rash or shock |
| Ceftriaxone | 2 g IV every 12 hours |
| Over 60 or immunosuppressed | Add amoxicillin for Listeria |
| Dexamethasone | 10 mg IV every 6 hours for 4 days, starting with the first antibiotic |
| Encephalitis | Aciclovir 10 mg/kg IV every 8 hours. Doses in the treatment section |
Check every dose against a current drug reference and your hospital protocol.
On this page
What it is
Meningitis is inflammation of the membranes around the brain and spinal cord, usually from infection. Encephalitis is inflammation of the brain itself, usually viral (herpes simplex is the one you must treat). They overlap: a patient can have both.
Common causes in adults:
- Bacteria: Streptococcus pneumoniae, Neisseria meningitidis (meningococcus), Listeria in older or immunosuppressed adults, Haemophilus influenzae.
- Viruses: enteroviruses (usually mild), herpes simplex (encephalitis).
- In Pakistan, also: tuberculous meningitis, cerebral malaria, and Naegleria fowleri (the "brain-eating amoeba") in Karachi and elsewhere in the hot months, linked to tap water used for nasal washing during ablution.
Recognising it
- Neck stiffness, light hurting the eyes
- Vomiting
- Mental state often normal early
- Non-blanching rash in meningococcal disease
- Confusion, strange behaviour, drowsiness
- Fits
- Focal signs: weakness, speech problems
- Neck may not be stiff
- The classic triad (fever, neck stiffness, confusion) is often incomplete. Absence of neck stiffness does not rule meningitis out.
- Kernig's and Brudzinski's signs are not sensitive. A negative test does not exclude meningitis.
- Non-blanching rash (press a glass on it): meningococcal disease until proven otherwise. The rash can start as ordinary-looking blanching spots.
- Older and immunosuppressed patients may have only confusion and fever.
Do not delay antibiotics
- Recognise possible bacterial meningitis.
- Blood cultures if they take no more than a few minutes.
- Dexamethasone and ceftriaxone within 1 hour (immediately if rash or shock).
- CT head only if indicated.
- LP as soon as safe, ideally within 1 hour of arrival. If the LP is delayed, antibiotics are not.
Antibiotics given before the LP reduce the chance of growing the organism, but PCR on the CSF and blood can still find it. The patient's life comes first.
CT before LP?
- GCS below 13 or falling
- Focal neurological signs
- Papilloedema
- New fits
- Immunosuppressed (HIV, chemotherapy, transplant)
- Suspected abscess or bleed
LP straight away, after antibiotics if there will be any delay
Do not do an LP if: signs of raised pressure, shock, a spreading purpuric rash, low platelets (below about 50,000/µL) or anticoagulation, infection at the LP site, or respiratory failure. See Lumbar puncture.
Treatment
- Severe penicillin allergy: senior and microbiology advice (chloramphenicol is an option where available).
- Supportive: oxygen, fluids for shock, sugar control, treat fits, head up 30 degrees if raised pressure is possible.
Reading the CSF
| Finding | Bacterial | Viral | Tuberculous |
|---|---|---|---|
| Appearance | Cloudy | Clear | Clear or slightly cloudy, may form a "cobweb" |
| White cells | High, mostly neutrophils | Raised, mostly lymphocytes | Raised, mostly lymphocytes |
| Protein | High | Normal or slightly high | Very high |
| CSF to blood glucose ratio | Low (below 0.4) | Normal (above 0.6) | Low |
| Opening pressure | High | Normal or slightly high | High |
Always send a blood glucose at the same time as the LP to compare. Ask for Gram stain, culture, bacterial PCR, HSV and enterovirus PCR, and TB tests (ZN stain, GeneXpert) if TB is possible.
Tuberculous meningitis
- Symptoms over weeks, not days: headache, fever, weight loss, behaviour change.
- Cranial nerve palsies (especially the sixth nerve), confusion, hydrocephalus on CT.
- CSF: lymphocytes, very high protein, low glucose.
- HIV, diabetes, known TB or contact.
Start anti-TB treatment with dexamethasone on clinical suspicion after senior advice. Waiting for culture can take weeks.
Naegleria fowleri
A rare but almost always fatal amoebic meningoencephalitis, reported every summer in Karachi. Suspect it in a previously healthy person with rapidly worsening meningitis, a history of nasal water exposure (ablution, swimming), and a CSF that looks bacterial with no organism. Tell your senior and the lab immediately: CSF wet mount can show moving amoebae.
Contacts and public health
- Meningococcal disease: notify public health. Close household contacts and anyone exposed to the patient's airway secretions (for example, during intubation without a mask) need prophylaxis.
- Droplet precautions for the first 24 hours of antibiotics.
After the acute phase
- Hearing test after bacterial meningitis, especially pneumococcal.
- Follow-up for memory, mood and neurological problems after encephalitis.
- Vaccination advice (pneumococcal, meningococcal) where relevant.
Common mistakes
- Waiting for the CT or LP before giving antibiotics.
- Forgetting dexamethasone, or giving it many hours after antibiotics.
- Forgetting amoxicillin for Listeria in the elderly and immunosuppressed.
- Missing encephalitis because the neck is not stiff, and not giving aciclovir.
- Not sending a blood glucose with the CSF.
- Thinking a blanching rash rules out meningococcal disease.
Frequently asked questions
What is the empirical antibiotic for bacterial meningitis in adults?
Ceftriaxone 2 g IV every 12 hours, plus amoxicillin 2 g IV every 4 hours if over 60, pregnant or immunosuppressed, and vancomycin where penicillin-resistant pneumococcus is likely.
When should dexamethasone be given in meningitis?
With or just before the first dose of antibiotics in suspected bacterial meningitis: 10 mg IV every 6 hours for 4 days, stopped if the cause is not bacterial.
When is a CT scan needed before lumbar puncture?
If the GCS is below 13 or falling, there are focal neurological signs, papilloedema, new fits, or the patient is immunosuppressed. Antibiotics are given first.
What does the CSF show in bacterial meningitis?
Cloudy fluid with high neutrophils, high protein, low glucose compared with blood, and high opening pressure.
Test yourself
Exam-style questions on this guide, from our two question banks. Choose an answer to see why each option is right or wrong.
1. A 19-year-old has fever, neck stiffness and a non-blanching rash. The CT scanner is busy for an hour. What should happen now?
Answer: IV ceftriaxone 2 g (with dexamethasone) immediately. Suspected bacterial meningitis or meningococcal sepsis: blood cultures if quick, then IV ceftriaxone without delay. Dexamethasone is given with or just before the first antibiotic dose.
- Paracetamol and review in 1 hour: Dangerous delay.
- Oral amoxicillin: Inadequate.
- Wait for CT, then LP, then antibiotics: Never delay antibiotics in suspected meningococcal disease.
- IV aciclovir only: Bacterial cover is essential.
2. A 72-year-old has suspected bacterial meningitis. What should be added to ceftriaxone?
Answer: IV amoxicillin. Cephalosporins do not cover Listeria. Add amoxicillin 2 g IV 4-hourly in older adults, the immunosuppressed and in pregnancy.
- Nothing extra: Listeria is more common over 50–60 years.
- Vancomycin for all: Only where pneumococcal resistance is common.
- Metronidazole: Anaerobes are not the concern.
- Gentamicin alone: Amoxicillin is the Listeria drug.
3. A patient has fever, confusion and a seizure, but no neck stiffness. Which drug must not be missed?
Answer: IV aciclovir. Fever with confusion, behaviour change or fits suggests herpes simplex encephalitis. Start IV aciclovir early; delay worsens outcomes.
- Oral valaciclovir: IV aciclovir is needed for encephalitis.
- IV metronidazole: Not indicated.
- IV phenytoin alone: Seizure control is needed but the cause must be treated.
- IV fluconazole: Not the likely cause.
4. A 19-year-old has fever, neck stiffness and photophobia. CSF shows turbid fluid, 1800 white cells/µL (90% neutrophils), protein 2.1 g/L and glucose ratio 0.2. What is the most likely cause?
Answer: Bacterial meningitis. Bacterial meningitis: turbid CSF, very high neutrophil count, high protein (> 1 g/L) and low glucose (CSF:plasma < 0.4). Viral: clear, lymphocytes, mildly raised protein, normal glucose. TB: lymphocytes, very high protein, low glucose, cobweb clot, subacute onset. Give IV ceftriaxone immediately (add ampicillin if > 50 years/immunosuppressed for Listeria), with dexamethasone before or with the first dose. Don’t delay antibiotics for imaging.
- Viral meningitis: Viral meningitis has lymphocytes and normal glucose.
- TB meningitis: TB meningitis has lymphocytes and a slower onset.
- Fungal meningitis: Fungal meningitis has lymphocytes and occurs in the immunosuppressed.
5. A young man in Karachi, who performs ablution by rinsing his nose with stored tap water, develops severe headache, fever, altered smell and rapidly progressive confusion. CSF shows neutrophils and motile trophozoites. What is the organism?
Answer: Naegleria fowleri. Primary amoebic meningoencephalitis: Naegleria fowleri (‘brain-eating amoeba’), a thermophilic free-living amoeba in warm freshwater and poorly chlorinated tanks/tap water; enters via the nose (swimming, nasal ablution/wudu, neti pots) → olfactory nerve → cribriform plate. Rapid fulminant meningoencephalitis (anosmia/parosmia early), death in ~1 week, > 95% fatal. Diagnosis: wet mount of CSF (motile trophozoites), PCR. Treatment: amphotericin B, miltefosine, azoles, rifampicin, cooling. Prevention: adequate chlorination; use boiled, filtered or sterile water for nasal rinsing.
- Acanthamoeba: Acanthamoeba causes subacute granulomatous encephalitis.
- Neisseria meningitidis: Meningococcus shows Gram-negative diplococci and a rash.
- Cryptococcus neoformans: Cryptococcus is a subacute encapsulated yeast, often in HIV.
6. A man with advanced HIV has fever and neck stiffness. India ink staining of the CSF shows round yeasts with clear halos. What is the organism?
Answer: Cryptococcus neoformans. Cryptococcus neoformans has a thick polysaccharide capsule, seen as a clear halo with India ink. It causes meningitis in people with CD4 counts below 100. The cryptococcal antigen test is more sensitive. Treat with amphotericin B and flucytosine, then fluconazole.
- Candida albicans: Forms pseudohyphae; not typical of meningitis.
- Histoplasma capsulatum: Small yeasts inside macrophages.
- Aspergillus fumigatus: Septate hyphae branching at 45 degrees.
- Mycobacterium tuberculosis: Acid-fast bacilli, no capsule halo.
7. Where is cerebrospinal fluid mainly absorbed back into the blood?
Answer: Arachnoid granulations. CSF is made mainly by the choroid plexus (about 500 mL a day), flows through the ventricles into the subarachnoid space, and is absorbed through arachnoid granulations (villi) into the superior sagittal sinus. Blockage of absorption causes communicating hydrocephalus.
- Choroid plexus epithelium: Produces CSF, it does not absorb it.
- Ependymal lining cells: Line the ventricles; minor role.
- Pial capillaries: Not the main route.
- Scalp lymphatics: Not a main route.
References and dose sources
- NICE NG240: Meningitis (bacterial) and meningococcal disease (2024)
- Encephalitis International
- Ceftriaxone dosing: Drugs.com: Ceftriaxone dosage (see also our ceftriaxone dose page)
- Dexamethasone dosing: Drugs.com: Dexamethasone dosage (see also our dexamethasone dose page)
- Amoxicillin dosing: Drugs.com: Amoxicillin dosage (see also our amoxicillin dose page)
- Vancomycin dosing: Drugs.com: Vancomycin dosage (see also our vancomycin dose page)
- Aciclovir dosing: Drugs.com: Acyclovir (aciclovir) dosage (see also our aciclovir dose page)
- Ciprofloxacin dosing: Drugs.com: Ciprofloxacin dosage (see also our ciprofloxacin dose page)
International guidance is linked where it reflects good practice. Where your hospital’s protocol differs, follow your hospital.