Definition of Meningitis:

Meningitis is a bacterial or non-bacterial infection that causes inflammation of the membranes covering the brain and spinal cord.

Causes, incidence, and risk factors:

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
• Carcinomatous meningitis (meningitis due to cancer)
• Cryptococcal meningitis
• Gram negative meningitis
• H. influenza 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 associated with enteroviruses, which are viruses that commonly cause intestinal illness.

Many other types of viruses can also 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 recurrent 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. In addition to causing viral meningitis, West Nile virus may cause encephalitis in some patients and a polio-like syndrome in others.