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Meningitis in Adults (cont.)

What Are Causes and Risk Factors of Meningitis in Adults?

Usually, the brain is protected naturally from the body's immune system by the barrier that the meninges create 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. Meningitis in children is becoming less common because children now receive the Hib vaccine in infancy as well as the pneumococcal vaccine (Prevnar).
  • 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.
  • Risk factors that place people at higher risk for bacterial meningitis include the following:
    • Adults older than 60 years of age
    • Children younger than 5 years of age
    • 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 in place for hydrocephalus
  • Fungal meningitis is a very serious and rare cause of meningitis. Typically limited to people who have had surgical procedures or have impaired immune systems due to cancer and other diseases affecting immune function, the 2012 outbreak of fungal meningitis was linked to a specific procedure using a specific steroid medication.
    • Other forms of steroids and steroid injections outside of the spine have not been implicated in fungal meningitis.
    • Fungal meningitis is not contagious and cannot be spread from person to person.
Medically Reviewed by a Doctor on 9/11/2017

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