Viral infections are the most common cause of meningitis. That's followed by bacterial infections and, rarely, fungal and parasitic infections. Because bacterial infections can lead to death, learning the cause is essential.
Bacterial meningitis
Bacteria that enter the bloodstream and travel to the brain and spinal cord cause bacterial meningitis. But bacterial meningitis also can occur when bacteria directly invade the meninges. This may be caused by an ear or sinus infection, a skull fracture, or — rarely — some surgeries.
Several strains of bacteria can cause bacterial meningitis, most commonly:
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Streptococcus pneumoniae. This bacterium is the most common cause of bacterial meningitis in infants, young children and adults in the United States. It more commonly causes pneumonia or ear or sinus infections. A vaccine can help prevent this infection.
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Neisseria meningitidis. This bacterium causes a bacterial meningitis called meningococcal meningitis. These bacteria commonly cause an upper respiratory infection but can cause meningococcal meningitis when they enter the bloodstream. This is a highly contagious infection that affects mainly teenagers and young adults. It may cause local epidemics in college dormitories, boarding schools and military bases.
A vaccine can help prevent infection. Even if vaccinated, anybody who has been in close contact with a person with meningococcal meningitis should receive an oral antibiotic to prevent the disease.
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Haemophilus influenzae.
Haemophilus influenzae type b (Hib) bacterium was once the leading cause of bacterial meningitis in children. But new
Hib vaccines have greatly reduced the number of cases of this type of meningitis.
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Listeria monocytogenes. These bacteria can be found in unpasteurized cheeses, hot dogs and lunchmeats. People who are pregnant, newborns, older adults and people with weakened immune systems are most susceptible. During pregnancy, listeria can cross the placenta. Infections in late pregnancy may be fatal to the baby.
Viral meningitis
Viral meningitis is usually mild and often clears on its own. Most cases in the United States are caused by a group of viruses known as enteroviruses. They're most common in late summer and early fall. Viruses such as herpes simplex virus,
HIV, mumps virus, West Nile virus and others also can cause viral meningitis.
Chronic meningitis
Chronic meningitis — one that's long-lasting — can be caused by slow-growing organisms such as fungi and Mycobacterium tuberculosis. They invade the membranes and fluid surrounding the brain. Chronic meningitis develops over two weeks or more. Symptoms are similar to acute meningitis, which is a sudden, new case. They include headache, fever, vomiting and mental cloudiness.
Fungal meningitis
Fungal meningitis isn't common in the United States. It may mimic acute bacterial meningitis. It's often contracted by breathing in fungal spores that may be found in soil, decaying wood and bird droppings.
Fungal meningitis isn't spread from person to person. Cryptococcal meningitis is a common fungal form of the disease. It affects people with weakened immune systems, such as from
AIDS. It can cause death if not treated with an antifungal medicine. Even with treatment, fungal meningitis may come back.
Parasitic meningitis
Parasites can cause a rare type of meningitis called eosinophilic meningitis. Parasitic meningitis also can be caused by a tapeworm infection in the brain or cerebral malaria. Amoebic meningitis is a rare type that is sometimes contracted through swimming in fresh water and can quickly become life-threatening.
The main parasites that cause meningitis typically infect animals. People are usually infected by eating foods contaminated with these parasites. Parasitic meningitis isn't spread between people.
Other meningitis causes
Meningitis also can result from noninfectious causes. They include chemical reactions, drug allergies, some types of cancer and inflammatory diseases such as sarcoidosis.