As the body tries to fight the infection, blood vessels become leaky and allow fluid, white blood cells, and other infection-fighting particles to enter the meninges and brain. This causes brain swelling and can eventually lead to decreasing blood flow to parts of the brain, making the symptoms of infection worse. Meningitis is usually caused by one of a number of bacteria. The most common is Streptococcus pneumoniae . Neisseria meningitidis can cause outbreaks in crowded conditions, such as college dormitories or military barracks.
Bacterial meningitis can occur for a number of reasons.
Meningitis can also be caused by spread of an infection occurring near the brain, such as from the ears or sinuses. It is also an occasional complication of brain surgery or head and neck surgery. The average age for meningitis is 25 years and affects both men and women equally. For unclear reasons, African Americans seem to get meningitis more frequently than people of other races. The remainder generally become ill over 1-7 days.