There are two main forms of meningitis:
- bacterial meningitis, and
- viral meningitis.
Bacterial meningitis affects fewer people than the viral form, but it often results in more serious health consequences. Bacterial meningitis is fatal in 1 in 10 cases and leaves 1 in 7 survivors with a severe disability caused by brain injury.
There are several types of bacterial meningitis. Two types represent the majority of bacterial meningitis cases:
The bacteria that cause these cases are common and live in the back of the nose and throat, or in the upper respiratory tract.
The bacteria are spread among people by coughing, sneezing and kissing. These bacteria cannot live outside the body for long, so they cannot be picked up from water supplies, swimming pools, or a building's air-conditioning system.
Individuals can carry these bacteria for days, weeks, or months without becoming ill. In fact, about 25 percent of the population carries the bacteria. Only rarely do the bacteria overcome the body's defenses and invade the cerebra spinal fluid, causing meningitis.
Meningococcal meningitis accounts for more than half of all cases of bacterial meningitis in the United States. Meningococcal disease is caused by bacteria called Neisseria meningitidis. There are several strains of Neisseria meningitidis. Strain B causes about 75 percent of the meningococcal cases and has the highest fatality rate.
Pneumococcal meningitis is caused by pneumococcus bacteria, which also cause several diseases of the respiratory system, including pneumonia. It has a fatality rate of about 20 percent. It also results in a higher incidence of brain damage than other forms of the disease.
Other types of bacterial meningitis include:
Neonatal meningitis: This form affects mostly newborn babies and is caused by Group B streptococcus bacteria, commonly found in the intestines.
Staphylococcal meningitis: This is a rare, but deadly form caused by staphylococcus bacteria. It usually develops as a complication of a diagnostic or surgical procedure.
Haemophilus influenza type B (Hib) is caused by haemophilus bacteria. It was once the most common form of bacterial meningitis, and one of the deadliest childhood diseases. However, in 1985, an Hib vaccine was introduced into the routine immunization program for U.S. children and virtually eliminated Hib meningitis in the United States.
Viral meningitis is far more common than the bacterial form and, in most cases, much less debilitating. Most people exposed to viruses that cause meningitis experience mild or no symptoms and fully recover without complications. '
The disease can be caused by many different viruses. Some of the viruses are transmitted by coughing or sneezing or through poor hygiene. Other viruses can be found in sewage polluted waters.
Occasionally, viral meningitis will develop following the mumps or chicken pox. Mosquito-born viruses also account for a few cases each year.
Approximately half of the viral cases in the United States are due to common intestinal viruses, or