Meningitis is an infection of the fluid (cerebrospinal fluid) and tissues (meninges) that surround the brain and spinal cord. Meningitis is usually caused by a virus or by bacteria.

Meningitis may start as a complication of another illness, such as a sinus or ear infection, or from an injury. Meningitis can be passed from person to person, and it can be mild or dangerous. A meningococcal vaccine is recommended for certain age groups and people with greater chances of getting infected. The vaccine helps prevent some types of meningitis.

Fungus is a common cause of meningitis in people with impaired immune systems (such as those with AIDS). In rare cases, meningitis may be caused by a parasite or an unexpected reaction to a medicine. Bacteria that cause meningitis can be passed from a pregnant woman to her baby during childbirth.

Treatment depends on the cause of the infection and how bad the illness is. Bacterial meningitis is usually more serious than viral meningitis. It is a medical emergency if a person has:

• A severe headache with stiff neck, fever, nausea, and vomiting.
• Severe sensitivity to light (photophobia).
• Extreme sleepiness.
• Confusion, restlessness, or irritability.
• Changes in vision.
• A bulging soft spot (fontanelle) on a baby's head and the baby is not crying.
• Seizures.