Bacterial meningitis is an infection of the membranes that cover the brain. It is caused by a bacteria.

What is going on in the body?

There are a number of different organisms that can cause bacterial meningitis. They generally begin growing in a person's nose and throat. If not stopped by the immune system, the bacteria go on to invade the body. They can enter the bloodstream and travel to the central nervous system.

The infection then settles in the fluid and the membranes around the brain. The resulting inflammation is responsible for many of the symptoms of meningitis. It may also play a role in some of the complications.

What are the causes and risks of the infection?

Bacterial meningitis is caused by a bacteria that usually enters the body through the person's nose or throat. The bacteria can be transmitted to newborns during labor and delivery. Many people can have the bacteria in their noses or throats without developing meningitis. The bacteria are more likely to cause meningitis in very young infants. People with a weakened immune system, such as those with AIDS, are also at high risk.