Meningitis is an infection and inflammation of the membranes (the meninges) surrounding the brain and spinal cord. It can be caused by a reaction to certain medications or medical treatments, an inflammatory disease such as lupus, some types of cancer, or a traumatic injury to the head or spine. The most common cause, however, is an infection by a virus, bacterium, parasite, or fungus.
Meningitis caused by an infection usually begins when the infection passes from its original site—for example, the upper respiratory tract—into the bloodstream and then into the cerebrospinal fluid that surrounds the brain and spinal cord. From there, it travels to the brain and/or the surrounding membranes, called the meninges. Sometimes the bacteria or viruses infect the meninges directly.
The seriousness of the infection and the best treatment depend on the cause. With bacterial meningitis, delaying treatment increases the risk for permanent brain damage or death. Viral meningitis, also called aseptic meningitis, is the most common form of meningitis in the United States. It is rarely fatal. Viral meningitis may also include inflammation of the brain itself.
The most common causes of bacterial meningitis are group B streptococcus, found in newborns; Haemophilus influenzae, now prevented with a vaccine; Streptococcus pneumoniae, which causes pneumococcal meningitis, the most common and serious form of this illness; and Neisseria meningitides, which causes meningococcal meningitis, a highly contagious form that is more likely to affect children and young adults. Less common bacterial causes are Listeria monocytogenes; Escherichia coli, which is more common in elderly adults and newborns; Mycobacterium tuberculosis; and Staphylococcus aureus.
Viral meningitis is usually caused by enteroviruses. These are common viruses that enter the body through the mouth and travel to the brain and surrounding tissues, where they multiply. Enteroviruses are present in mucus, saliva, and feces and can be transmitted through direct contact with an infected person or an infected object or surface.
Viruses that can cause meningitis include varicella zoster, the virus that causes chickenpox and shingles; influenza viruses, mumps virus, HIV, arboviruses, which cause diseases such as West Nile and eastern equine encephalitis; and herpes simplex virus. Fungi and parasites also can cause meningitis.
Signs and symptoms
The early signs and symptoms of meningitis are easily mistaken for the flu, the National Meningitis Association says. They may develop over a period of a day or two, but some types of meningitis can prove fatal within 24 hours after symptoms appear.
Seek medical care right away if someone has any of these signs or symptoms:
Several risk factors can make you or your child more likely to be infected with meningitis:
Age. Newborns of mothers infected with group B strep, children younger than 5 years, and young adults ages 18 to 24 are at higher risk. (Elderly adults also are at higher risk.)
Living in a community setting. College students living in dormitories, personnel on military bases and children in boarding schools and child-care facilities are at increased risk for meningitis.
Other factors, including AIDS, diabetes, and use of immunosuppressant drugs, also make a person more susceptible to meningitis.
Most viral meningitis is a seasonal illness. It's more common during the summer and early fall than at other times of the year.
The complications of meningitis can be severe and include hearing loss, blindness, learning disabilities, brain damage, and paralysis. Whether complications occur depends on a person's age, his or her immunity, the type of bacteria, virus, or other pathogen involved, and how quickly treatment is started.
The earlier that bacterial meningitis is treated, the better the chances of full recovery. Antibiotics are the usual treatment, and many cases may be treated with intravenous antibiotics.
Viral meningitis cannot be treated with antibiotics, which are only effective against bacteria. For a mild case of viral meningitis, the best treatment is usually extra fluids, rest in a darkened room, and medication for pain and fever. A more severe case of viral meningitis may be treated in the hospital. Some types of viral meningitis can be treated with antiviral medications.
The most serious forms of meningitis are those caused by bacteria and spread from person to person. These include meningococcal meningitis, Haemophilus influenzae, and pneumococcal meningitis. Vaccines for the latter two are now part of routine childhood immunizations. Immunization against meningococcal meningitis is recommended for middle and high school students and college freshmen living in dormitories. It is also recommended for children and adults ages 2 through 50—those who travel to countries where meningitis is widespread, those who have an immune system disorder, and those who have a damaged spleen or whose spleen has been removed.
You can cut your risk of picking up meningitis from an infected person by following good personal hygiene. You should avoid sharing food, utensils, drinking glasses, and other personal objects with a person who has meningitis. When in contact with an infected person, be sure to wash your hands often with soap and water.
West Nile encephalitis, a form of meningoencephalitis, affecting both the brain and meninges, is spread by mosquitoes. You can prevent this illness by staying indoors in early morning or at dusk, when mosquitoes feed. When outdoors, use a mosquito repellant. Place screens on your windows to prevent mosquitoes from entering your home.