Meningitis is inflammation of the meninges (the membranes that protect the brain and spinal cord) due to infection by viruses, bacteria or fungi.

Viral (aseptic) meningitis is the most common type of the disease. However, symptoms of viral meningitis tend to be very mild with many cases going unnoticed or undiagnosed. Therefore, the exact number of viral meningitis cases that occur each year is unknown. Bacterial meningitis is far less common than viral meningitis, although it tends to be much more dangerous and can be fatal if not treated promptly.

A variety of signs and symptoms (e.g., fever, headache) may indicate a mild meningitis infection, with most subsiding after a few days. Symptoms of a more serious meningitis infection (e.g., seizures, vomiting) require immediate medical attention. In most cases, meningitis can be diagnosed from a complete medical history, physical examination and certain medical tests (e.g., spinal tap, imaging tests).

Treatment of meningitis is dependent on its type or cause. Some common treatments for viral meningitis include rest, over-the-counter medications and fluid consumption. Bacterial meningitis is typically treated with antibiotics. The combinations prescribed depend on the infection source, severity and age of the patient, among other variables. Vaccinations are available to prevent some forms of bacterial meningitis. Avoiding viruses that cause viral meningitis may also reduce the risk of infection.