Meningitis is inflammation of the protective membranes covering the brain and spinal cord, known collectively as the meninges. The inflammation may be caused by infection with viruses, bacteria, or other microorganisms, and less commonly by certain drugs.
Meningitis can be life-threatening because of the inflammation's proximity to the brain and spinal cord; therefore the condition is classified as a medical emergency.
The most common symptoms of meningitis are headache and neck stiffness associated with fever, confusion or altered consciousness, vomiting, and an inability to tolerate light (photophobia) or loud noises (phonophobia).
Sometimes, especially in small children, only nonspecific symptoms may be present, such as irritability and drowsiness. If a rash is present, it may indicate a particular cause of meningitis; for instance, meningitis caused by meningococcal bacteria may be accompanied by a characteristic rash.
A lumbar puncture may be used to diagnose or exclude meningitis. This involves inserting a needle into the spinal canal to extract a sample ofcerebrospinal fluid (CSF), the fluid that envelops the brain and spinal cord.
The CSF is then examined in a medical laboratory. The usual treatment for meningitis is the prompt application of antibiotics and sometimes antiviral drugs. In some situations, corticosteroid drugs can also be used to prevent complications from overactive inflammation.
Meningitis can lead to serious long-term consequences such as deafness, epilepsy, hydrocephalus andcognitive deficits, especially if not treated quickly. Some forms of meningitis (such as those associated with meningococci, Haemophilus influenzaetype B, pneumococci or mumps virus infections) may be prevented by immunization.
The classic signs and symptoms of meningitis are headache, fever, and stiff neck (in adults and older children). Symptoms of meningitis may appear suddenly and can also include nausea and vomiting.
Changes in behavior, such as confusion, sleepiness, and difficulty waking up, are other important symptoms. In infants, symptoms of meningitis are often much less specific and may include irritability or tiredness, poor feeding, and fever.
Some types of meningitis can be deadly if not treated promptly. Anyone experiencing symptoms of meningitis should see a doctor immediately.
There are several types of bacterial meningitis.
Two types represent the majority of bacterial meningitis cases:
The bacteria that cause these cases are common and live in the back of the nose and throat, or in the upper respiratory tract.
The bacteria are spread among people by coughing, sneezing and kissing. These bacteria cannot live outside the body for long, so they cannot be picked up from water supplies, swimming pools, or a building's air-conditioning system.
Individuals can carry these bacteria for days, weeks, or months without becoming ill. In fact, about 25 percent of the population carries the bacteria. Only rarely do the bacteria overcome the body's defenses and invade the cerebra spinal fluid, causing meningitis.
Meningococcal meningitis accounts for more than half of all cases of bacterial meningitis in the United States. Meningococcal disease is caused by bacteria called Neisseria meningitidis. There are several strains of Neisseria meningitidis. Strain B causes about 75 percent of the meningococcal cases and has the highest fatality rate.
Pneumococcal meningitis is caused by pneumococcus bacteria, which also cause several diseases of the respiratory system, including pneumonia. It has a fatality rate of about 20 percent. It also results in a higher incidence of brain damage than other forms of the disease.
Other types of bacterial meningitis include:
Neonatal meningitis: This form affects mostly newborn babies and is caused by Group B streptococcus bacteria, commonly found in the intestines.
Staphylococcal meningitis: This is a rare, but deadly form caused by staphylococcus bacteria. It usually develops as a complication of a diagnostic or surgical procedure.
Haemophilus influenza type B (Hib) is caused by haemophilus bacteria. It was once the most common form of bacterial meningitis, and one of the deadliest childhood diseases. However, in 1985, an Hib vaccine was introduced into the routine immunization program for U.S. children and virtually eliminated Hib meningitis in the United States.
Viral meningitis is far more common than the bacterial form and, in most cases, much less debilitating. Most people exposed to viruses that cause meningitis experience mild or no symptoms and fully recover without complications.
The disease can be caused by many different viruses. Some of the viruses are transmitted by coughing or sneezing or through poor hygiene. Other viruses can be found in sewage polluted waters.
Occasionally, viral meningitis will develop following the mumps or chicken pox. Mosquito-born viruses also account for a few cases each year.
Approximately half of the viral cases in the United States are due to common intestinal viruses, or enteroviruses. These viruses are shed in the feces and in discharges from the mouth and nose. Most people who become infected with the virus contract it through hand-to-mouth contact.
Because meningitis can cause serious damage in a short amount of time, anyone suspected of having meningitis should get immediate treatment. For bacterial meningitis, strong doses of intravenous antibiotics are required.
Viruses cannot be killed by antibiotics, so most treatment for viral meningitis does not involve medications to kill the virus. Depending on the source of infection, infected sinuses may need to be drained as part of treatment.
Early treatment for bacterial meningitis is important for people with the disease. Bacterial meningitis treatment involves strong doses of intravenous antibiotics. Antibiotics may also be given to prevent other bacterial infections.
Corticosteroids such as prednisone may be used to relieve brain pressure and swelling, and to prevent hearing loss that is common in patients with Haemophilus influenzae meningitis. Pain medicine and sedatives may be given to make patients more comfortable.
Depending on the source of infection, infected sinuses may need to be drained as part of treating meningitis.
Appropriate treatment for most types of meningitis can reduce the risk of dying from the disease to below 15 percent.