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Meningitis normally occurs as a complication from an infection in the bloodstream. A barrier (called the blood-brain barrier) normally protects the brain from contamination by the blood. Sometimes, infections directly decrease the protective ability of the blood-brain barrier. Other times, infections release substances that decrease this protective ability.
Once the blood-brain barrier becomes leaky, a chain of reactions can occur. Infectious organisms can invade the fluid surrounding the brain. The body tries to fight the infection by increasing the number of white blood cells (normally a helpful immune system response), but this can lead to increased inflammation. As the inflammation increases, brain tissue can start swelling and blood flow to vital areas of the brain can decrease.
Meningitis can also be caused by the direct spread of a nearby severe infection, such as an ear infection (otitis media) or a nasal sinus infection (sinusitis). An infection can also occur any time following direct trauma to the head or after any type of head surgery.
* Bacterial meningitis can be caused by many different types of bacteria. Certain age groups are predisposed to infections of specific types of bacteria.
* Viral meningitis is much less serious than bacterial meningitis and frequently remains undiagnosed because its symptoms are similar to the common flu. The frequency of viral meningitis increases slightly in the summer months because of greater exposure to the most common viral agents, called enteroviruses. (emedicinehealth)
Once the blood-brain barrier becomes leaky, a chain of reactions can occur. Infectious organisms can invade the fluid surrounding the brain. The body tries to fight the infection by increasing the number of white blood cells (normally a helpful immune system response), but this can lead to increased inflammation. As the inflammation increases, brain tissue can start swelling and blood flow to vital areas of the brain can decrease.
Meningitis can also be caused by the direct spread of a nearby severe infection, such as an ear infection (otitis media) or a nasal sinus infection (sinusitis). An infection can also occur any time following direct trauma to the head or after any type of head surgery.
* Bacterial meningitis can be caused by many different types of bacteria. Certain age groups are predisposed to infections of specific types of bacteria.
- Immediately after birth, bacteria called group B Streptococcus, Escherichia coli, and Listeria species are the most common.
- After approximately age 1 month, bacteria called Streptococcus pneumoniae, Haemophilus influenzae type B (Hib), and Neisseria meningitidis are more frequent. The widespread use of the Hib vaccine as a routine childhood immunization is dramatically decreasing the frequency of meningitis caused by Hib.
* Viral meningitis is much less serious than bacterial meningitis and frequently remains undiagnosed because its symptoms are similar to the common flu. The frequency of viral meningitis increases slightly in the summer months because of greater exposure to the most common viral agents, called enteroviruses. (emedicinehealth)
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