Meningitis is an infection and inflammation of the membranes (meninges) and fluid (cerebrospinal fluid) surrounding your brain and spinal cord. Meningitis is most often caused by bacteria or viruses. Bacterial meningitis is usually much more serious than viral meningitis. Most cases of meningitis occur when bacteria from an infection in another part of your body travel through your bloodstream to your brain and spinal cord. But bacteria can also spread directly to your brain or spine from a severe head injury or from an infection in your ear, nose or teeth.

Some types of meningitis are contagious. You may be exposed to the bacteria when someone with meningitis coughs or sneezes. The bacteria can also spread through kissing or sharing eating utensils, a toothbrush or a cigarette. You're also at increased risk if you live or work with someone with the disease.

Meningitis strikes suddenly, usually with a high fever, severe headache and vomiting. As the disease progresses, the brain swells and may begin to bleed. Meningitis is fatal in about 10 percent of cases. Unfortunately, many of those who survive an attack may have serious long-term neurologic complications, such as deafness, blindness, speech loss or brain damage.

Seventy percent of meningitis cases occur in children under age 5, but the incidence of the disease is increasing among young people between the ages of 15 and 24. Older adults also tend to have a high incidence of meningitis.

Meningitis is a medical emergency. How well you recover depends on how quickly you receive treatment. If you suspect that you or someone in your family has symptoms of meningitis, seek medical care right away.

Signs and symptoms

It's easy to mistake the early symptoms of bacterial and viral meningitis for the flu. These symptoms may develop over a period of 1 or 2 days, but some types of meningitis can prove fatal in a matter of hours. Even in less severe cases, the longer you delay getting treatment, the more likely you are to have permanent neurologic damage. Seek medical care right away if you or anyone in your family has any of the following signs or symptoms:

• A high fever that prevents you from eating or drinking

• Severe headache

• vomiting

• Confusion

• Seizures

• Progressive lethargy

• Drowsiness

• Stiff neck

• An accompanying skin rash, especially near your armpits or on your hands or feet

• Rapid progression of small hemorrhages under your skin

• Sensitivity to light

Symptoms in newborns

Newborns and young infants may not have the classic symptoms of headache, fever and stiff neck. Instead, they may cry constantly, seem unusually sleepy or irritable, and eat poorly. Sometimes the soft spots on their head may bulge. Babies who are very ill may actually have a lower than normal temperature. A very late symptom may be a spasm consisting of extreme hyperextension of the body (opisthotonos).

Causes

Most meningitis is caused by either bacteria or viruses. But the disease can also result from a fungal infection, a blow to the head, some types of cancer, inflammatory diseases such as lupus, or a sensitivity reaction to certain medications — especially ibuprofen (Advil, Motrin, others) and an infusion of gamma globulins used to treat other conditions.

Bacterial meningitis

A number of types of bacteria can cause acute bacterial meningitis. They include:

• Pneumococcus. This bacterium is the most common cause of meningitis in adults and children. It most often occurs when the bacterium Streptococcus pneumoniae (pneumococcus) enters your bloodstream and migrates to your brain and spinal cord. You may also have this type of bacteria in your lungs, where it causes pneumonia. Pneumococcal meningitis can also result from an ear infection.

• Meningococcus. This bacterium is another common cause of meningitis in children under age 5, in teens and in young adults. The incidence of meningococcal meningitis is increasing among college-aged students, especially those living in dormitories. According to the Centers for Disease Control and Prevention (CDC), the number of cases among 15- to 24-year-olds doubled between 1991 and 1997. Meningococcal meningitis commonly occurs when bacteria from an upper respiratory infection enter your bloodstream. It's highly contagious and may cause localized epidemics in college dormitories, boarding schools and on military bases. Five strains of the Neisseria meningitidis bacterium cause meningococcal meningitis: A, B, C, Y and W-135. A vaccine is available that offers some protection against all but serogroup B. The vaccine is effective for only 3 to 5 years, however. In 1999, the CDC recommended that all college students, especially those living on campus, receive the vaccine.

• Haemophilus. The Haemophilus influenzae (H. influenzae) bacterium was once the leading cause of bacterial meningitis in children under age 5. But widespread use of the Hib vaccine has greatly reduced the number of cases of this type of meningitis. When it occurs, it tends to follow an upper respiratory infection, ear infection (otitis media) or sinusitis. Rates of H. influenzae meningitis and pneumococcal meningitis are highest among black, American Indian and Eskimo children, who may not have access to preventive medical care. Children in child-care settings are also at higher risk.

• Listeria. Listeria monocytogenes can be found almost anywhere — in soil, in dust and in foods that have become contaminated with these bacteria. In the past, contaminated foods have included soft cheeses, hot dogs and luncheon meats. Many wild and domestic animals also carry the bacteria. Fortunately, most healthy people exposed to listeria don't become ill, although pregnant women, newborns and older adults are especially susceptible. In fact, pregnant women have a 20 times greater risk of becoming ill from this bacterium than other adults do. Listeria crosses the placental barrier, and infections in late pregnancy may cause a baby to be stillborn or die shortly after birth. In adults and children older than 2 weeks of age, exposure to the listeria bacterium can cause meningitis.

Acute bacterial meningitis also can occur when bacteria invade the meninges directly, rather than through the bloodstream. Common causes include ear or sinus infections and skull fractures.

Viral meningitis

Also called aseptic meningitis, viral meningitis is usually mild and often clears on its own in 1 to 2 weeks. Common intestinal viruses cause about half the cases. Viruses associated with mumps, herpes infection or other diseases can also cause viral meningitis. In some cases, you or your child may pick up viral meningitis from polluted water.

Chronic meningitis

Chronic (ongoing) forms of meningitis occur when slow-growing organisms such as the microorganisms that cause tuberculosis invade the membranes and fluid surrounding your brain. Although acute meningitis strikes suddenly, chronic meningitis develops over weeks or months. Nevertheless, the symptoms of chronic meningitis — headaches, fever, vomiting and mental cloudiness — are similar to those of acute meningitis.

Fungal meningitis

Cryptococcal meningitis is a fungal form of the disease that affects about 10 percent of people with AIDS. Although cryptococcal meningitis can be effectively treated with antifungal medications, it tends to recur in nearly half of those affected. In these cases, doctors may recommend long-term antifungal therapy with drugs such as fluconazole (Diflucan).

Risk factors

Children under age 5, young people ages 18 to 24 and older adults are more likely to develop meningitis than the rest of the population. Black, Eskimo and American Indian children are especially at risk of meningitis caused by the bacteria H. influenzae and Streptococcus pneumoniae. People with weakened or suppressed immune systems also are at higher risk.

College students living in dormitories, personnel on military bases and children in boarding schools and child-care facilities are at increased risk of meningococcal meningitis, mainly because infectious diseases tend to spread quickly wherever large groups of people congregate.

If you're pregnant, you're 20 times more likely to contract listeriosis, an infection that may cause meningitis. If you have listeriosis, your unborn baby is at risk too. Also at higher risk of listeriosis are people who work with domestic animals, including dairy farmers and ranchers.

Some studies have linked increased risk to smoking and drinking alcohol, which may suppress your body's immune system. Other factors that may compromise your immune system — including AIDS, diabetes and use of immunosuppressant drugs — also make you more susceptible to meningitis. Removal of your spleen, an important part of your immune system, may also increase your risk.

When to seek medical advice

The sooner you're treated for acute bacterial meningitis, the better are the chances that you'll recover without serious complications. But the disease can make you sick very quickly. If you or someone in your family has symptoms of meningitis — such as fever, severe headache, vomiting and stiff neck — get medical care right away.

If a family member or someone you work with has meningitis, talk to your doctor about medications that can help prevent you from getting sick.

Screening and diagnosis

Your doctor will likely diagnose meningitis based on your medical history, a physical exam and certain diagnostic tests. During the exam, your doctor may check for signs of infection around your head, ears, throat and the skin along your spine.

You may also have a throat culture to check for the bacteria that cause meningitis, perhaps X-rays or a computerized tomography (CT) scan of your chest, skull or sinuses. A CT scan is a diagnostic imaging procedure that uses a series of very thin computer-generated X-rays to reveal two-dimensional "slices" of your body.

The definitive diagnosis of meningitis, however, is often made by analyzing a sample of your cerebrospinal fluid (CSF), which is extracted during a procedure known as a spinal tap (lumbar puncture). After you've received a local anesthetic, your doctor inserts a thin, hollow needle between two vertebrae in your lower back (lumbar area) and into your spinal canal. He or she then removes some cerebrospinal fluid for laboratory analysis. One of the signs of meningitis is a low sugar (glucose) level along with an increased white blood cell count in the fluid. CSF analysis may also help your doctor identify the exact bacteria that's causing your illness.

The entire procedure takes from less than 10 to about 30 minutes. You may have a feeling of pressure while the fluid is being extracted and a headache afterward because of a drop in CSF pressure. A lumbar puncture also carries a small risk of infection.

If your doctor suspects you have viral meningitis, he or she may order a test known as a polymerase chain reaction (PCR) amplification to check for the presence of certain viruses. If you have chronic meningitis caused by cancer or an inflammatory illness, you may need other tests. In all cases, however, your doctor's goal will be to make an accurate diagnosis and start treatment as soon as possible.

Complications

The complications of meningitis can be severe. The longer you have the disease without treatment, the greater your risk of seizures and of permanent neurologic damage, such as hearing loss, brain damage, blindness, loss of speech, learning disabilities and behavior problems.

Non-neurologic complications may include kidney and adrenal gland failure. Your adrenal glands produce a number of important hormones, including cortisone, which helps your body deal with stress.

Bacterial infections of your central nervous system progress quickly. Within hours of the onset of symptoms, the disease can lead to shock and death.

Treatment

Acute bacterial meningitis requires prompt treatment with intravenous antibiotics to ensure recovery and reduce your risk of complications. The antibiotic or combination of antibiotics used depends on the type of bacteria causing your meningitis. Often, analyzing a sample of your cerebrospinal fluid can help identify the bacteria. In some cases, your doctor may start you on a general antibiotic until he or she can determine the exact cause of your meningitis. You may also be given corticosteroids to help prevent hearing loss, one of the most common complications of the disease.

Sometimes you may need to be treated for brain swelling, shock, convulsions or dehydration. Infected sinuses or mastoids — the bones behind your outer ear that connect to your middle ear — may need to be drained. Any fluid that has accumulated between your brain and the membranes that surround it may also need to be drained or surgically removed.

Mild cases of viral meningitis are usually treated with bed rest, plenty of fluids and sometimes analgesics to help reduce your fever and relieve body aches. If your meningitis is caused by the herpes virus, your doctor would likely recommend an available herpes group antiviral medication. Not all viruses that cause meningitis have antiviral agents available for use.

Prevention

Although immunizations provide protection from some types of meningitis, you can also help reduce your risk by avoiding exposure to upper respiratory and gastrointestinal infections. In fact, something as simple as careful hand washing may be one of the best ways to stay well.

Teach your children to wash their hands often, especially before they eat and after using the bathroom, spending time in a crowded public place or petting animals. Show them how to wash their hands vigorously, covering both the front and back of each hand with soap and rinsing thoroughly under running water.

In addition, boost your immune system by getting enough rest, exercising regularly, and eating a healthy diet with plenty of fresh fruits, vegetables and whole grains. If you're pregnant, cook meat thoroughly and avoid cheeses made from unpasteurized milk.

Immunizations

Many children now routinely receive vaccines against H. influenzae and pneumococcal meningitis, starting at about 2 months of age. Immunizations are recommended by the American Academy of Pediatrics and many other organizations. If your child hasn't been vaccinated, talk to your doctor or clinic about the Hib and pneumococcal (Prevnar 7) vaccines for your child.

A vaccine also is available that offers some protection against four of the five strains of bacteria responsible for meningococcal meningitis. Both the Centers for Disease Control and Prevention and the American College Health Association (ACHA) recommend the vaccine for college students, especially those living in campus dormitories. Because this vaccine may not be widely available, check with your student health service. The vaccine is also recommended for people traveling to countries where meningitis is common. It's important to receive the vaccine at least 1 week before your departure.

To help protect against pneumonia, all adults over age 65 should receive the pneumonia vaccine. The vaccine is also recommended if you have a chronic illness such as heart disease, diabetes or sickle cell anemia or have a compromised immune system.