Meningitis is an infection of the meninges, the membranes that cover and protect the brain and spinal cord, and the cerebrospinal fluid (CSF) that cushions the brain. The meninges also prevent the CSF from leaking. Most cases of meningitis are caused by viruses and are usually mild; meningitis caused by bacteria, however, is a serious disease and can
be fatal. Meningitis occurs when disease organisms that have entered the body and multiplied in the nose, mouth, and throat get into the bloodstream and are carried to the meninges. In a few cases meningitis can develop when the bacteria gain entrance to the body through a surgical incision or an injury to the head or neck.
Doctors sometimes divide cases of meningitis into three categories according to the speed of symptom development. Acute meningitis develops in less than twenty-four hours and is usually caused by one of several species of bacteria; it is considered a medical emergency. Subacute meningitis takes between one and seven days for symptoms to appear; it may be caused by bacteria or viruses. Chronic meningitis develops over a period of more than a week and may result from an infection or a non-infectious cause.
The central symptoms of meningitis are a high fever, headache, and stiff neck, resulting from the swelling caused by the inflammation of the meninges. Most patients also have nausea and vomiting, mental confusion, extreme sensitivity to light, chills, and rapid breathing.
Viral meningitis, which is also called aseptic meningitis, is a less severe infection than bacterial meningitis and may not require any specific treatment. It is caused by one or more enteroviruses, which are viruses that normally live in the digestive tract. Viral meningitis usually develops in the late summer and early fall, and is most likely to affect children and adults under the age of thirty. Most viral infections occur in children under the age of five. Enteroviruses are present in saliva, throat mucus, and feces; they can be transmitted through direct contact with an infected person or an infected object or surface. Viral meningitis can also be caused by the viruses that cause chickenpox, mumps, HIV infection, West Nile virus infection, and genital herpes.
Bacterial meningitis is a medical emergency and has a high mortality rate if untreated. It is spread by coughing, kissing, and contact with an infected person's saliva. There are several different types of bacteria that can cause meningitis including Streptococcus pneumoniae, the pneumococcus that is most common in adults, and Neisseria meningitides, the meningococcus that is more common in children and teenagers. Persons who have had pneumococcal meningitis may be left with lifelong damage to their nervous system that includes deafness and brain damage.
Less common forms of bacterial meningitis are caused by Listeria, a bacterium that can cause the death of a baby before birth as well as meningitis; and meningitis caused by Mycobacterium tuberculosis, the bacterium responsible for tuberculosis. Haemophilus influenzae, a bacterium that was at one time thought to be the cause of flu, used to be the most common cause of bacterial meningitis in the United States; however, the introduction of a vaccine against this organism in 1990 has greatly lowered the number of cases.
Meningitis caused by fungi is rare in the general population but is a fairly common opportunistic infection in patients with AIDS.
According to the Centers for Disease Control and Prevention (CDC), there are two to three cases of bacterial meningitis for every 100,000 persons in the United States each year. About 6,000 cases of pneumococcal meningitis are reported each year, and 2,600 cases of meningococcal meningitis.
Risk factors for bacterial meningitis include:
- Age. Since the introduction of childhood vaccines, bacterial meningitis is now more common in young adults.
- Group-living situations. These may include military bases, college dormitories, and child care centers.
- Having a weakened immune system. People with AIDS or diabetes are at increased risk of meningitis.
- Working with animals. Farmers and others who work with animals have an increased risk of Listeria infections.
- Sex. Among newborns, boys are three times more likely than girls to get meningitis. Among adults, men and women are equally likely to be infected.
Most cases of meningitis are caused by disease organisms—viruses, bacteria, or fungi—that enter the bloodstream and are carried to the brain and the meninges. A few cases of meningitis result from inflammatory diseases like lupus or certain cancers.
The most important symptoms used to diagnose meningitis are a high fever, stiff neck, and severe headache, which may come on in less than a day after infection. Other symptoms in adults may include:
- Nausea and vomiting
- Extreme sensitivity to light
- Confusion and difficulty concentrating
- Loss of appetite
- Drowsiness or difficulty waking up
- Skin rash (more common with meningococcal meningitis)
Infants and small children may have somewhat different symptoms:
- Bulging of the soft spot at the top of an infant's skull
- Constant crying
- Poor feeding
- Unusual sleepiness
- Stiffness in the baby's body as well as neck
Diagnosis of the cause of meningitis is essential to proper treatment, as the antibiotics used to treat bacterial meningitis are not useful in treating viral meningitis. A patient who has acute bacterial meningitis will usually have treatment started as soon as the doctor obtains a sample of cerebrospinal fluid for testing. The CSF is obtained by performing a spinal tap, a procedure in which a needle is inserted into an area in the lower back where the doctor can easily obtain a sample of fluid.
A patient with subacute meningitis may be given a physical examination to check for an ear, throat, or sinus infection. The doctor may also perform two maneuvers to see whether the patient's meninges are inflamed. In one test, the doctor raises the patient's leg at the hip to a right angle from the examining table and tries to straighten the lower leg. If the leg cannot be straightened or the patient experiences neck pain, he
or she most likely has meningitis. The other maneuver involves bending the patient's neck forward as they lie on the table. If the knees and hips flex upward, the patient probably has meningitis. The doctor may also order an x ray or computed tomography (CT) scan of the head and neck to look for swelling and inflammation.
The sample of CSF is sent to a laboratory for analysis. Identification of the specific bacterium can take several days, meanwhile, the doctor can begin to treat the patient with a broad-spectrum antibiotic until the test results come back.
In 2007 the Food and Drug Administration (FDA) approved a rapid CSF test that identifies virus particles in CSF in about three hours. This test allows doctors to distinguish fairly quickly between viral and bacterial meningitis and avoid giving unnecessary antibiotics to patients with viral meningitis.
It is important to get a patient with the symptoms of meningitis to a hospital as quickly as possible, particularly if the symptoms appeared in less than a day. Patients who are acutely ill and are taken to a hospital are usually treated within thirty minutes of their arrival, as emergency room doctors assume that the patient has bacterial meningitis and do not want to delay treatment until the specific organism is identified. A sample of cerebrospinal fluid is taken by a spinal tap for analysis; then the patient is given intravenous penicillin or another broad-spectrum antibiotic, intravenous fluids, and pure oxygen to assist breathing. The patient may also need to be treated for seizures, or to have fluid drained from the sinuses or from the space between the meninges and the brain. After the specific bacterium has been identified, the doctor can adjust the type and dosage of the antibiotics given to the patient.
Viral meningitis cannot be treated with antibiotics. Patients are usually advised to stay home and rest in bed for a few weeks. They can take over-the-counter pain relievers for muscle aches and pains and to bring down fever. If the viral meningitis is caused by the herpes virus, the doctor may also prescribe acyclovir, an antiviral drug used to treat herpes.
Acute bacterial meningitis has a mortality rate of 10–15 percent even with treatment. Pneumococcal meningitis may have a mortality rate as
high as 21 percent. Of the patients who survive, between 10 and 20 percent will suffer such complications as blindness, hydrocephalus, hearing loss, learning disorders, or even paralysis.
Viral meningitis is usually a much milder disease. Some patients may need to be hospitalized for supportive care for a week or so, but most can recover at home within two weeks. Complications are rare with viral meningitis.
There are several vaccines that can be used to prevent meningitis. As has already been mentioned, the rates of Haemophilus influenzae meningitis among young children dropped dramatically after a vaccine against this bacterium was added to childhood immunization schedules in the 1990s. There are also vaccines that have been developed to protect adults as well as children from pneumococcal and meningococcal meningitis. There is one type of pneumococcal vaccine known as PCV7, recommended for children between two and five years of age who are at high risk of infection. A different vaccine known as PPV is recommended for adults at risk of pneumococcal meningitis: those over sixty-five, those with weakened immune systems, those with diabetes or heart disease, and those whose spleen was removed. The vaccine that protects against the meningococcus is known as MCV4. It is recommended for all children at eleven and twelve and for college students who were not vaccinated at that age. MCV4 can also be used to protect people exposed to meningitis during an outbreak or who must travel to countries with high rates of meningococcal meningitis.
Other preventive measures that people can take include:
- Keep the immune system strong by getting enough sleep, exercising regularly, and eating a healthy diet.
- Wash the hands regularly, particularly when living in a dormitory or similar housing situation.
- Avoid sharing glasses, drinking cups, food utensils, and similar items with others who may be infected or exposed to infection.
- Cover the mouth or nose before sneezing or coughing.
- Take any antibiotics that may be prescribed during a meningitis outbreak in one's school or workplace.
- Ask the doctor about vaccination before traveling abroad.
Meningitis is likely to continue to be a health problem for the foreseeable future. There are parts of the world, such as Brazil, southeastern Asia, and Africa below the Sahara, where meningitis epidemics still occur. In addition, the bacteria and viruses that cause most cases of meningitis are commonplace organisms that are hard to avoid. The development of effective vaccines is helping to lower the rates of meningitis in the United States. At present, researchers are looking at new medications that may help to lower the rates of complications from bacterial meningitis as well as studying several new vaccines.
SEE ALSO AIDS; Encephalitis; Genital herpes; Hearing loss; Hydrocephalus; Lupus
WORDS TO KNOW
Aseptic meningitis: A term that is sometimes used for meningitis that is not caused by bacteria.
Hydrocephalus: Abnormal accumulation of cerebrospinal fluid within the cavities inside the brain.
Meninges (singular, meninx): The membranes that cover the brain and spinal cord.
Opportunistic infection: An infection caused by an organism that does not cause disease in a person with a healthy immune system.
Goldsmith, Connie. Meningitis. Minneapolis, MN: Twenty-First Century Books, 2008.
Centers for Disease Control and Prevention (CDC). Meningococcal Disease—Frequently Asked Questions. Available online at http://www.cdc.gov/meningitis/bacterial/faqs.htm (accessed September 24, 2008).
Mayo Clinic. Meningitis. Available online at http://www.mayoclinic.com/health/meningitis/DS00118 (accessed September 24, 2008).
National Institute of Neurological Disorders and Stroke (NINDS). Meningtitis and Encephalitis Fact Sheet. Available online at http://www.ninds.nih.gov/disorders/encephalitis_meningitis/detail_encephalitis_meningitis.htm (accessed September 24, 2008).
National Library of Medicine (NLM). Meningitis. Available online at http://www.nlm.nih.gov/medlineplus/tutorials/meningitis/htm/index.htm (accessed September 24, 2008). This is an online tutorial with voiceover; viewers have the option of a self-playing version, an interactive version with questions, or a text version.
PBS NOVA. Killer Disease on Campus. Available online at http://www.pbs.org/wgbh/nova/meningitis/ (accessed September 24, 2008). Site includes a set of five animations about the spread of bacterial meningitis through the body. Each animation takes about a minute to play.
TeensHealth. Meningitis. Available online at http://kidshealth.org/teen/infections/bacterial_viral/meningitis.html (accessed September 24, 2008).