Meningitis and Encephalitis

The answer first

Central nervous system infection is a time-critical medical emergency. The single decision that determines outcome is: start empiric antibiotics and antivirals the moment you suspect the diagnosis, before lumbar puncture, before CT, before any delay. A patient with suspected bacterial meningitis who waits for a CT scan before antibiotics has a measurably worse outcome ^[2].

The empiric regimen for a community-acquired CNS infection in an immunocompetent adult is: ^[1]

1. Ceftriaxone 2 g IV every 12 hours plus vancomycin (covering penicillin-resistant pneumococcus and meningococcus)
2. Add ampicillin 2 g IV every 4 hours if the patient is over 50, pregnant, alcoholic, or immunocompromised (covers Listeria monocytogenes)
3. Aciclovir 10 mg/kg IV every 8 hours if encephalitis is possible (fever with altered mental status, seizures, or focal neurology)
4. Dexamethasone 10 mg IV every 6 hours given before or with the first antibiotic dose if bacterial meningitis is suspected — especially pneumococcal ^[1]

Meningitis (inflammation of the meninges) presents with fever, headache, and neck stiffness. Encephalitis (inflammation of the brain parenchyma) presents with fever plus altered mental status, seizures, or focal neurological deficits. The distinction matters because the empiric therapy and the differential are different. Many patients have meningoencephalitis — overlap of both. ^[1]

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References14ShowHide

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