Meningitis is swelling and irritation (inflammation) of the membranes covering the brain and spinal cord. This inflammation causes changes in the cerebrospinal fluid (CSF) that surrounds the brain and spinal cord.

See also:

• Aseptic meningitis
• Meningitis - gram-negative
• Meningitis - H. influenzae
• Meningitis - meningococcal
• Meningitis - pneumococcal
• Meningitis - staphylococcal
• Meningitis - tuberculous

The most common causes of meningitis are viral infections that usually get better without treatment. However, bacterial meningitis infections are extremely serious, and may result in death or brain damage even if treated.

Meningitis is also caused by:

• Chemical irritation
• Drug allergies
• Fungi
• Tumors

Types include:

• Aseptic meningitis
• Cryptococcal meningitis
• Gram negative meningitis
• H. influenza meningitis
• Meningitis due to cancer (carcinomatous meningitis)
• Meningococcal meningitis
• Pneumococcal meningitis
• Staphylococcal meningitis
• Syphilitic aseptic meningitis
• Tuberculous meningitis

Acute bacterial meningitis is a true medical emergency, and requires immediate treatment in a hospital.

Viral meningitis is milder and occurs more often than bacterial meningitis. It usually develops in the late summer and early fall, and often affects children and adults under age 30. Most infections occur in children under the age of 5. Most viral meningitis is due to enteroviruses, which are viruses that also cause intestinal illness.

Many other types of viruses can cause meningitis. For example, viral meningitis can be caused by herpes viruses, the same virus that can cause cold sores and genital herpes (although people with cold sores or genital herpes are not at a greater risk of developing herpes meningitis).

Recently, West Nile virus, spread by mosquito bites, has become a cause of viral meningitis in most of the United States.