sections include: bacterial meningitis, viral and other types of meningitis, diagnosis and treatment
Meningitis is an infection or inflammation of the lining over the brain and spinal cord (the meninges) and in the fluid produced by that lining (cerebrospinal fluid, or CSF). Often people fear meningitis because some forms can be contagious and rapidly fatal. Fortunately, other kinds are much less harmful, and the disorder remains relatively uncommon in the United States. Each year there are only about 2 cases in every 100,000 people.
Different types of microorganisms can cause meningitis. The infections produced by bacteria are often the most acute and severe and can be fatal. Viral meningitis is much more common and much less severe; it usually does not require treatment and leaves no lasting effects. Unusual types of meningitis, such as that caused by fungal infections, occur primarily in people whose immune systems are weakened. All these microorganisms can infect other parts of our bodies as well; it is just by chance that in some cases they infect the meninges and CSF.
Symptoms of meningitis appear rapidly, over hours or a few days. They usually include fever and headache; over 90 percent of people diagnosed with the disease report these symptoms. People with meningitis will often complain that light hurts their eyes (photophobia) and may complain of a stiff neck (meningismus). Some may vomit. Over time, the sufferer may become restless and irritable and might develop seizures and experience neurological problems such as weakness, hearing loss or visual changes. Over 80 percent of people experience some sort of neurological symptom.
In severe cases, a person with meningitis may lapse into a coma. In the very young and the very old, meningitis symptoms may be much subtler, making diagnosis more difficult. In newborns, elevated CSF pressure may cause a bulge in the fontanels (the gaps between the developing bones of the skull) or hydrocephalus.
The danger of bacterial meningitis, and the ease with which it spreads, varies greatly depending on the bacterium involved.
Only one form of meningitis is truly contagious—an infection by the bacterium Neisseria meningitidis, also called meningococcus. This form of bacterial meningitis accounts for about 25 percent of cases in the United States, most occurring in children and young adults. Of all the people who contract meningitis from N. meningitidis, only 3 percent die. Because the disease is potentially contagious, people who come into close contact with someone infected with meningococcus, such as members of the same household, are often given prophylactic antibiotics such as rifampin to halt its spread and prevent disease.
Meningococcal meningitis outbreaks have occurred in crowded settings, such as day-care centers, army barracks, and dormitories, because it is airborne (caught and spread through coughing). The disease also occurs in epidemics in some areas of the world, such as sub-Saharan Africa.
A meningococcal vaccine is available for four types of N. meningitidis infections—A, C, Y, and W135. Physicians give this vaccine when one of these four types might cause an outbreak in susceptible people, such as military recruits, college students in the United States and abroad, and travelers spending long periods in crowded conditions in high-risk areas of the world. It is not recommended as a routine vaccination in the United States because many of the sporadic cases here involve N. meningitidis type B, which is not prevented by the current vaccine.
Until 1985, most cases of bacterial meningitis occurred in children under 5 years old (up to 60 cases per 100,000 children each year). The overwhelming majority of these infections, about 10,000 cases a year, were caused by Haemophilus influenzae type b (Hib). This kind of meningitis has a 6 percent mortality rate. Since 1985, when the first Hib vaccine became available to all children starting at two months of age, the incidence of Hib meningitis has declined by 90 percent. The vaccine has been improved recently to be even more effective. In parts of the world where the vaccine is not available, Hib meningitis remains a devastating disease of childhood and is mildly contagious among very close contacts, particularly other children.
Streptococcus pneumoniae (pneumococcus) is the most common cause of meningitis in adults, although it can also affect children and the elderly. This bacterium can cause a more severe disease than others, with the highest overall mortality—21 percent. Like the other organisms, it usually reaches the meninges through a person’s breathing, or it follows an infection in the blood. Pneumococcal meningitis, too, can be prevented and reduced through a vaccine, which is recommended for high-risk individuals over the age of 2. These individuals include the elderly and people with underlying disease such as cancer, diabetes, kidney disease, AIDS, and lung and heart disease. A new formulation pneumococcal vaccine has recently become available to protect high-risk children under 2; it may become a routine vaccination in all children, similar to the improved Hib vaccine.
Specific groups of people may contract less common forms of bacterial meningitis. Newborns can get meningitis from Group B streptococcus picked up while passing through the birth canal of an infected mother. Newborns can also get meningitis from gut flora such as Escherichia coli and Klebsiella. These bacteria, as well as Staphylococcus aureus, can also cause meningitis in individuals who have had severe head trauma or neurosurgical procedures. Listeria monocytogenes is a less common bacterium that can cause meningitis in people whose immune systems are compromised, as well as in the elderly. It is usually acquired by eating contaminated foods such as cheese and other dairy products. Other bacterial diseases that in rare cases cause meningitis include syphilis (Treponema pallidum), Lyme disease (Borrelia burgdorferi), pneumonia (Mycoplasma pneumoniae), Rocky Mountain spotted fever (Rickettsia rickettsii), brucellosis, nocardiosis, and tuberculosis (Mycobacterium tuberculosis).
Viral and Other Types of Meningitis
Viruses account for over half of all cases of meningitis, generally causing a much less severe form of the disease than bacteria. Viral meningitis usually lasts 7 to 14 days and is associated with headache, a stiff neck, and fever. Most cases occur in late summer and early fall and are caused by one of the many enteroviruses belonging to the Coxsackie or ECHO families. However, many other viruses, including mumps, herpes simplex II, and even HIV, can produce viral meningitis. Each virus spreads in its normal, characteristic way. Various fungi and parasites can cause meningitis if they infect the spinal column. These cases of meningitis are uncommon and are more likely to occur in people whose immune systems are compromised because of other diseases. Each type has its own specific treatment, and physicians must also bear in mind the infected person’s other possible health problems.
Diagnosis and Treatment
Doctors diagnose meningitis by examining the individual and by testing his or her cerebrospinal fluid. They obtain the CSF through a procedure called a lumbar puncture, or spinal tap. The person usually lies on his or her side, often curled in a fetal position. The doctor or nurse cleans the lower spine well and applies a local anesthetic to numb the area. The physician then inserts a needle between the patient’s L3 and L4 vertebrae and draws out a sample of CSF. The fluid is sent to a laboratory for testing.
Typically, meningitis produces an inflammation that causes a higher than usual CSF pressure, white blood cell count, and protein level. In viral meningitis, testing the spinal fluid reveals a mild elevation of white blood cells, primarily in mononuclear cells. In bacterial meningitis, there is also likely to be an increased number of neutrophils (a specific type of white blood cell) and a somewhat lower sugar level.
Doctors can have a person’s CSF cultured to check for bacteria, including tuberculosis; viruses; or fungi. The fluid may also be tested to identify less common causes of meningitis, such as syphilis and cryptococcus. Recent advances have made it possible for doctors to diagnose some specific types of meningitis within hours of testing.
The quicker a person receives treatment for bacterial meningitis, the better. In fact, if doctors even suspect bacterial meningitis, they usually perform a spinal tap immediately and start therapy before receiving the test results. If they cannot do the spinal tap for some reason, they give antibiotics immediately anyway. Bacterial meningitis is truly a case of “Better safe than sorry.”
Treating Bacterial Meningitis
Treating bacterial meningitis consists of giving high-dose intravenous antibiotics that penetrate the meninges and spread in high levels through the CSF and brain tissue. Only certain antibiotics get through the meninges adequately. It is therefore very important that doctors use the appropriate antibiotics. Initially doctors use a combination of antibiotics to cover all possible causes, but once they have identified the exact cause of the meningitis they can use specific therapy against it. In children who have Hib meningitis, the use of steroids in conjunction with antibiotics has been shown to reduce the risk of hearing loss.
Meningitis can be fatal because it can cause severe neurological damage that, in some cases, cannot be reversed by treatment. For people who survive the infection, bacterial meningitis may leave lasting effects. Newborns and young children may have mild to severe learning disabilities, as well as significant hearing loss, seizures, blindness, or other neurological deficits.
Treating Viral Meningitis
While physicians have treatments for bacterial and fungal meningitis, we cannot yet treat the viral form directly. (This is equally true for many other viral diseases, starting with the common cold.) Instead, doctors focus on alleviating a person’s symptoms and reducing discomfort. This treatment includes pain relief and fever control. The rate of death or disability associated with viral meningitis is minimal, and the condition usually leaves no lasting effects. New antiviral agents to treat viral meningitis, such as pleconaril, are being tested but are not yet available.
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