Meningitis

Definition

Meningitis is an infection that causes inflammation of the membranes covering the brain and spinal cord. Non-bacterial meningitis is often referred to as "aseptic meningitis." Bacterial meningitis may be referred to as "purulent meningitis."

Causes, incidence, and risk factors

The most common causes of meningitis are viral infections that usually resolve without treatment. However, bacterial infections of the meninges are extremely serious illnesses, and may result in death or brain damage even if treated. Meningitis is also caused by fungi, chemical irritation, drug allergies, and tumors.

Types include:

• Meningitis - cryptococcal
• Syphilitic aseptic meningitis
• Meningitis - H. influenza
• Meningitis - meningococcal
• Meningitis - pneumococcal
• Meningitis - staphylococcal
• Meningitis - tuberculous
• Aseptic meningitis
• Meningitis gram negative
• Carcinomatous meningitis (meningitis due to cancer)

Acute bacterial meningitis is a true medical emergency, and requires immediate hospital-based treatment. Bacterial strains that cause meningitis include Streptococcus pneumoniae, Haemophilus influenzae, Neisseria meningitidis (meningococcus), Listeria monocytogenes, and many other types of bacteria. In the U.S. about 17,500 cases of bacterial meningitis occur each year.

Viral meningitis is milder and occurs more often than bacterial meningitis. It usually develops in the late summer and early fall, often affects children and adults under 30. Seventy percent of the infections occur in children under the age of 5. Most viral meningitis is associated with enteroviruses, which are viruses that commonly cause intestinal illness.

However, many other types of viruses can also cause meningitis. For example, viral meningitis may occur as a complication in people with genital herpes. Recently, West Nile virus spread by mosquito bites has become a cause of viral meningitis in most of the U.S. In addition to causing viral meningitis, West Nile virus may cause encephalitis in some patients and a polio-like syndrome in others.

Symptoms

• Fever and chills
• Severe headache
• Nausea and vomiting
• Stiff neck (meningismus)
• Sensitivity to light (photophobia)
• Mental status changes

Additional symptoms that may be associated with this disease:

• Decreased consciousness
• Rapid breathing
• Agitation
• Opisthotonos (severe neck stiffness, ultimately resulting in a characteristic arched posture-seen in infants or small children)
• Bulging fontanelles (the soft spots in a baby's skull may bulge)
• Poor feeding or irritability in children

Meningitis is an important cause of fever in newborn children. For this reason, a lumbar puncture is often done on newborns who have a fever of uncertain origin.

Signs and tests

• Lumbar puncture with CSF glucose measurement and CSF cell count
• Gram-stain and culture of CSF (cerebral spinal fluid)
• Chest x-ray to look for other sites of infection
• Head CT scan looking for hydrocephalus, abscess or deep swelling

Treatment

Antibiotics will be prescribed for bacterial meningitis; the type will vary depending on the infecting organism. Antibiotics are not effective in viral meningitis. Treatment of secondary symptoms including brain swelling, shock, and seizures will require other medications and intravenous fluids. Hospitalization may be required depending on the severity of the illness and the needed treatment.

Expectations (prognosis)

Early diagnosis and treatment of bacterial meningitis is essential to prevent permanent neurological damage. Viral meningitis is usually not serious, and symptoms should disappear within 2 weeks with no residual complications.

Complications

• Hearing lossor deafness
• Brain damage
• Loss of vision
• Hydrocephalus

Calling your health care provider

If you feel that you or your child have symptoms suggestive of meningitis, you must seek emergency medical help immediately. Early treatment is key to a good outcome.

Prevention

• Haemophilus vaccine (HiB vaccine) in children will help prevent one type of meningitis.
• The pneumococcal conjugate vaccine is now a routine childhood immunization and is very effective at preventing pneumococcal meningitis.
• It is highly recommended that household contacts and people with close contact with individuals with meningococcal meningitis receive preventative antibiotics to avoid becoming infected themselves.
• Some communities conduct vaccination campaigns following an outbreak of meningococcal meningitis. Military recruits are routinely vaccinated against this form of meningitis because of its high rate of occurrence.
• The American Academy of Pediatrics and the American College Health Association encourage college students (particularly freshmen living in dormitories) to consider being vaccinated with the meningococcal vaccine.

Illustrations

Brudzinski's sign of meningitis

Kernig's sign of meningitis

Lumbar puncture (spinal tap)

Meninges of the brain

Meninges of the spine

Haemophilus influenza organism

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