Meningitis
Inflammation of the meninges, most dangerously from bacterial invasion of the normally sterile subarachnoid space, where speed of antibiotic delivery, not diagnostic certainty, determines survival.
First principles
Meningitis is inflammation of a normally protected, immune-privileged space
The subarachnoid space and its cerebrospinal fluid are normally sterile and defended by the blood-brain barrier, with relatively low baseline levels of complement and antibody. Once organisms breach this barrier (by haematogenous spread from nasopharyngeal colonisation, or by direct spread from sinusitis, otitis media or a skull fracture), the weak local immune surveillance allows rapid bacterial proliferation, explaining why bacterial meningitis can progress from first symptom to critical illness within hours.
Educational content pending clinical review. Not medical advice.