meningitis

Inflammation of the meninges (membranes) surrounding the brain, caused by bacterial or viral infection. Bacterial meningitis, though treatable by antibiotics, is the more serious threat. Diagnosis is by lumbar puncture.

Bacterial meningitis is caused by Neisseria meningitidis, a bacterium that colonizes the epithelial lining of the throat and is carried by 2–10% of the healthy population. Illness results if the bacteria enters the bloodstream, but this is rare.

Many common viruses can cause the occasional case of meningitis, although not usually in its more severe form. The treatment for viral meningitis is rest.

There are three strains of bacterial meningitis: serogroups A, B, and C. Vaccines exist for A and C, while clinical trials of candidate vaccines for meningitis B began in 2001. However, the existing vaccines do not provide long-term protection nor are they suitable for children under the age of two. B is the most prevalent of the groups, causing over 50% of cases in Europe and the USA. The severity of the disease varies from mild to lethal, and symptoms include fever, headache, nausea, neck stiffness, delirium, and (rarely) convulsions.