Meningitis

Definition

Meningitis is an infection of the meninges and cerebral spinal fluid (CSF) caused by viruses , bacteria, or fungi. The meninges are the membranes that cover the brain and spinal cord. CSF is clear liquid that surrounds and helps protect the brain and spinal cord.

Description

Meningitis can be caused by the spread of viruses, bacteria, or fungi into the cerebral spinal fluid. These pathogens can invade the CSF directly, but are more likely reach the meninges by traveling through the bloodstream from an infection in another part of the body. Infections of the ear or sinuses are particularly likely to result in meningitis. The severity of the disease varies from mild to fatal depending on the cause.

Viral meningitis is the most common form of the disease, and it is also the mildest. Except for newborns, most people who develop viral meningitis recover completely within 7–10 days. In newborns, viral meningitis can be fatal. In the United States, about 10,000 cases of viral meningitis are reported each year, although some experts believe that the actual rate is ten times higher. Because many people recover from mild viral meningitis without treatment, many cases go unreported.

Bacterial meningitis is uncommon, but it is the most dangerous form of the disease. Left untreated, it is always fatal. Even when successfully treated it can cause permanent damage to the nervous system that can result in hearing loss , vision loss, and on-going seizures. The incidence of bacterial meningitis has dropped dramatically in the developed world since the 1990s because of routine immunization against the three most common types of bacteria that cause meningitis. In parts of the world where access to medical care is limited, bacterial meningitis is common and remains a significant cause of death , especially young children.

Fungal meningitis is uncommon. It occurs most often in people with compromised immune systems, especially individuals with AIDS . Drug allergies , certain autoimmune diseases, and some types of cancer can also cause inflammation of the meninges or noninfectious meningitis.

Demographics

Although anyone can develop meningitis, it is most likely to occur among newborns and children under age 5 who have not been vaccinated and adolescents ages 15–24. The very old are also at higher risk for contracting the disease. People who live group settings such as nursing homes, assisted living facilities , dormitories, military bases, or prisons are more likely to contract the disease. Meningitis is contagious and spreads easily through people living in close contact. Individuals who work with domestic animals, such as cattle and sheep, are at higher risk for contracting meningitis caused by listeria bacteria, although most people exposed to this bacterium, which is found in soil, dust, and on animals, do not become sick. People with diseases that weaken the immune system , such as diabetes or AIDS, those taking drugs that suppress immune system functioning, and people who have had their spleen (a part of the immune system) removed are also at higher risk.

Causes and symptoms

About 90% of cases of viral meningitis is caused by viruses from the enterovirus family. Viruses from this family also cause viral gastritis (stomach flu). However, viruses that cause mumps, measles, and polio can also cause viral meningitis. Although these diseases are uncommon in developed countries, they are still prevalent in the developing world and may be of concern to travelers.

Bacterial meningitis is caused primarily by four types of bacteria.

• Streptococcus pneumoniae. This is also called pneumococcal meningitis. The bacterium also causes pneumonia, ear, and sinus infections. It is a leading cause of bacterial meningitis in young children.
• Neisseria meningitidis. Also called meningococcal meningitis, this bacterium is highly contagious and is often responsible for outbreaks of meningitis among young adults.
• Haemophilus influenzae. Routine childhood vaccinations against Haemophilus bacteria have been available since the 1990s and in the developed world have substantially reduced this cause of meningitis.
• Listeria monocytogenes. Pregnant women and older adults are at higher risk than other groups for contracting listeria meningitis. Listeria can cross the placenta and kill a developing fetus.

Symptoms for all types of meningitis usually develop suddenly within one or two days, and are similar. Symptoms include an excruciating headache, stiff neck, substantial fever, nausea, vomiting, seizures, confusion, and lethargy. These symptoms often, but not always, follow another type of infection (e.g., respiratory, ear, sinus). Individual who develop these symptoms need immediate medical care. It is not possible to tell the cause of the meningitis from symptoms alone. Untreated bacterial meningitis can cause death within two days, so it is necessary to treat all suspected meningitis as if it has a bacterial cause until proven differently.

Diagnosis

Bacterial meningitis is definitively diagnosed by finding bacteria in the CSF. A sample of CSF is obtained by a lumbar puncture (spinal tap), examined under the microscope, and cultured to determine the type of bacteria present. The results can take up to one week. In 2007, the United States Food and Drug Administration (FDA) approved a rapid test for viral meningitis called the Xpert EV test. Using a sample of CSF, this test can accurately identify about 90% of viral meningitis cases in less than three hours. Since bacterial meningitis is often fatal, if no virus is found in the CSF, the disease is treated as if it is caused by bacteria until proven otherwise.

Treatment

There is no cure for viral meningitis. Symptoms such as pain , fever, and dehydration are treated. Young children may need to be hospitalized. With supportive care, most people recover within two weeks with no lasting complications.

Bacterial meningitis is treated immediately in a hospital with intravenous (IV) antibiotics . The specific antibiotic depends on the type of bacterium causing the infection. Until that determination is made, a broad-spectrum antibiotic that kills the most common types of bacteria is administered. People with bacterial meningitis may need additional treatment for shock, seizures, dehydration, and brain swelling. Serious cases of bacterial meningitis may require treatment in an intensive care unit (ICU) and life support.

Prognosis

With the exception of newborns and people with severely suppressed immune systems, few people die from viral meningitis and fewer than 1% have any complications from the disease.

Untreated bacterial meningitis is fatal. When treated with antibiotics, about 75% of patients recover, although the exact rate varies depending on the specific bacterium causing the infection. Pneumococcal meningitis has the highest death rate. Lasting complications from bacterial meningitis occur among about one-quarter of those who recover.

Prevention

Viral meningitis cannot be prevented. Its spread can be reduced by good hygiene practices such as frequent hand washing and not sharing personal items. Immunization is the best defense against bacterial meningitis. Vaccines are available that protect against Haemophilus influenzae. type b (Hib vaccine), pneumococcal meningitis (PCV7 vaccine for young children, PPV vaccine for older children and adults), and meningococcal meningitis (MCV4).

QUESTIONS TO ASK YOUR DOCTOR

• Do I need to be hospitalized?
• If I have viral meningitis how long will it take for me to get back to my normal daily activities?
• What sort of complications should I look for if I have bacterial meningitis? Can they be prevented?
• Are there immunizations I can have to help prevent bacterial meningitis?
• Can other people catch this disease from me?

Caregiver concerns

Caregivers of the elderly, especially those living in group situations such as nursing homes, should encourage their charges ask their healthcare provider whether vaccines against meningitis are appropriate for them.

Resources

BOOKS

Beers, Mark H., Robert S. Porter, and Thomas V. Jones, eds. “Acute Bacterial Meningitis.” In The Merck Manual, 18th ed. Whitehouse Station, NJ: Merck, 2007. http://www.merck.com/mmhe/sec06/ch089/ch089b.html.

Goldman, Lee and Dennis Ausiello., eds. Cecil Textbook of Medicine., 23rd ed. Philadelphia Saunders Elsevier, 2008.

Goldsmith, Connie Meningitis, new ed. Minneapolis, MN: Twenty-First Century Books, 2008.

Harrison's Principles of Internal Medicine, 17th ed. New York, NY: McGraw-Hill, 2008.

ICON Health Publications. Bacterial Meningitis: A Medical Dictionary, Bibliography, and Annotated Research Guide to Internet References. San Diego, CA: ICON Health Publications, 2004.

Marcovitz, Hal. Meningitis. San Diego., CA: ReferencePoint Press, 2008.

PERIODICALS

Torpy, Janet M. “Meningitis.” Journal of the American Medical Association. 297 no. 1 (January 3, 2007.): 122. http://jama.ama-assn.org/cgi/reprint/297/1/122.pdf.

OTHER

“Meningitis.” Mayo Clinic.com. February 5, 2008 [cited April 2, 2008]. http://www.mayoclinic.com/health/meningitis/DS00118.

“Meningitis.” MedlinePlus. April 2, 2008 [cited April 3, 2008]. http://www.nlm.nih.gov/medlineplus/meningitis.html.

Razonable, Robert. “Meningitis.” eMedicine.com. November 26,2007 [cited April 2, 2008]. http://www.emedicine.com/med/TOPIC2613.HTM.

Vokshoor, Amir. “Viral Meningitis”. August 23, 2007 [cited April 2, 2008]. http://www.emedicine.com/neuro/TOPIC607.HTM.

ORGANIZATIONS

Meningitis Research Foundation, Midland Way, Thornbury, Bristol,, BS35 2B5, 01454 281811, 01454 281094, http://www.meningitis.org.

National Institute of Allergy and Infectious Diseases Office of Communications and Government Relations, 6610 Rockledge Drive, MSC 6612, Bethesda, MD, 20892-6612, (301) 496-5717, (866) 284-4107 or TDD: (800) 877-8339 (for hearing impaired), (301) 402-3573, http://www3.niaid.nih.gov.

United States Centers for Disease Control and Prevention (CDC), 1600 Clifton Road, Atlanta, GA, 30333, (404) 639-3534, (800) 311-3435, [email protected], http://www.cdc.gov.

Helen Davidson