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Causes
By Mayo Clinic staff
Meningitis usually results from a viral infection, but the cause may also be a bacterial infection. Less commonly, a fungal infection may cause meningitis. Because bacterial infections are the most serious and can be life-threatening, identifying the source of the infection is an important part of developing a treatment plan.
Bacterial meningitis
Acute bacterial meningitis usually occurs when bacteria enter the bloodstream and migrate to the brain and spinal cord. But it can also occur when bacteria directly invade the meninges, as a result of an ear or sinus infection or a skull fracture.
A number of strains of bacteria can cause acute bacterial meningitis. The most common include:
- Streptococcus pneumoniae (pneumococcus). 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.
- Neisseria meningitidis (meningococcus). This bacterium is another leading cause of bacterial meningitis. Meningococcal meningitis commonly occurs when bacteria from an upper respiratory infection enter your bloodstream. This infection is highly contagious. It affects mainly teenagers and young adults, and may cause local epidemics in college dormitories, boarding schools and military bases.
- Haemophilus influenzae (haemophilus). Before the 1990s, Haemophilus influenzae type b (Hib) bacterium was the leading cause of bacterial meningitis in children. But new Hib vaccines — available as part of the routine childhood immunization schedule in the United States — have greatly reduced the number of cases of this type of meningitis. When it occurs, it tends to follow an upper respiratory infection, ear infection (otitis media) or sinusitis.
- Listeria monocytogenes (listeria). These bacteria can be found almost anywhere — in soil, in dust and in foods that have become contaminated. Contaminated foods have included soft cheeses, hot dogs and luncheon meats. Many wild and domestic animals also carry the bacteria. Fortunately, most healthy people exposed to listeria don't become ill, although pregnant women, newborns and older adults tend to be more susceptible. Listeria can cross the placental barrier, and infections in late pregnancy may cause a baby to be stillborn or die shortly after birth. People with weakened immune systems, due to disease or medication effect, are most vulnerable.
Viral meningitis
Each year, viruses cause a greater number of cases of meningitis than do bacteria. Viral meningitis is usually mild and often clears on its own within two weeks. A group of viruses known as enteroviruses are responsible for about 30 percent of viral meningitis cases in the United States. As many viral meningitis episodes never have a specific virus identified as the cause.
The most common signs and symptoms of enteroviral infections are rash, sore throat, diarrhea, joint aches and headache. These viruses tend to circulate in late summer and early fall. Viruses such as herpes simplex virus, La Crosse virus, West Nile virus and others also can cause viral meningitis.
Chronic meningitis
Chronic forms of meningitis occur when slow-growing organisms invade the membranes and fluid surrounding your brain. Although acute meningitis strikes suddenly, chronic meningitis develops over two weeks or more. Nevertheless, the signs and symptoms of chronic meningitis — headaches, fever, vomiting and mental cloudiness — are similar to those of acute meningitis. This type of meningitis is rare.
Fungal meningitis
Fungal meningitis is relatively uncommon and causes chronic meningitis. Occasionally it can mimic acute bacterial meningitis. Cryptococcal meningitis is a common fungal form of the disease that affects people with immune deficiencies, such as AIDS. It's life-threatening if not treated with an antifungal medication.
Other meningitis causes
Meningitis can also result from noninfectious causes, such as drug allergies, some types of cancer and inflammatory diseases such as lupus.
- Meningitis questions & answers. Centers for Disease Control and Prevention. http://www.cdc.gov/meningitis/about/faq.html. Accessed June 8, 2010.
- Tunkel AR. Clinical features and diagnosis of acute bacterial meningitis in adults. http://www.uptodate.com/home/index.html. Accessed June 1, 2010.
- Meningitis and encephalitis fact sheet. National Institute of Neurological Disorders and Stroke. http://www.ninds.nih.gov/disorders/encephalitis_meningitis/detail_encephalitis_meningitis.htm. Accessed June 8, 2010.
- Johnson RP. Aseptic meningitis in adults. http://www.uptodate.com/home/index.html. Accessed June 8, 2010.
- Meningococcal vaccines: What you need to know. Centers for Disease Control and Prevention. http://www.cdc.gov/vaccines/pubs/vis/downloads/vis-mening.pdf. Accessed June 8, 2010.
- FDA approves the first vaccine to prevent meningococcal disease in infants and toddlers. FDA. http://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm252392.htm. Accessed April 27, 2011.
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