Adult Meningitis Causes

Usually, the brain is protected naturally from the body's immune system by the barrier the meninges creates between the bloodstream and the brain itself. Normally, this helps prevent the body from mounting an immune reaction to attack itself. In meningitis, however, this can become a problem.

Once bacteria or other organisms have found their way to the brain, they are somewhat isolated from the immune system and can spread. However, when the body eventually begins to fight the infection, the problem can worsen.

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 the brain. This causes brain swelling and can eventually lead to decreased blood flow to parts of the brain, worsening the symptoms of infection.

• 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. Haemophilus influenzae type B (Hib) can also cause meningitis in adults and children, but it is becoming less common because children now receive the Hib vaccine in infancy.

• Bacterial meningitis can occur for a number of reasons. Often, it is the result of an infection by bacteria that already live in the nose and mouth. The bacteria enter the blood and become lodged in the brain's outer covering, the meninges.

• Meningitis can also be caused by the spread of an infection occurring near the brain, such as from the ears or the sinuses. It is also an occasional complication of brain, head, or neck surgery.

• The average age for meningitis is 25 years, and meningitis affects both men and women equally. For unclear reasons, African Americans seem to develop meningitis more frequently than do people of other races.

• Those people at greater risk for meningitis than the rest of the population include the following:
  
  
  • Adults older than 60 years
    
    
  • Children younger than 5 years
    
    
  • People with alcoholism
    
    
  • People with sickle cell anemia
    
    
  • People with cancer, especially those receiving chemotherapy
    
    
  • People who have received transplants and are taking drugs that suppress the immune system
    
    
  • People with diabetes
    
    
  • Those recently exposed to meningitis at home
    
    
  • People living in close quarters (military barracks, dormitories)
    
    
  • IV drug users
    
    
  • People with shunts for hydrocephalus