Meningitis is inflammation of the meninges that results in swelling of brain tissue and sometimes spinal tissue (spinal meningitis). Swelling inhibits the flow of blood and oxygen to brain tissue. The characteristic symptoms of meningitis are stiff neck, severe headache, and fever.
The meninges are three ultrathin membranes that surround and protect the brain and a portion of the spinal cord: the outer membrane (dura mater), middle membrane (arachnoid), and inner membrane (pia mater).
Meningitis is either infectious (contagious) or noninfectious. Infectious meningitis is classified as viral, bacterial, fungal, or parasitic, depending on the type of organism causing the infection.
Viral meningitis, also called aseptic meningitis, is the most common type. It is rarely fatal and usually resolves with treatment. Meningitis develops in fewer than 1 in 1000 people who are infected with one of the viruses associated with the condition.
Bacterial meningitis is often severe and is considered a potential medical emergency. If left untreated, bacterial meningitis may be fatal or cause serious long-term complications. Because bacterial meningitis can progress rapidly, it is important to identify the bacteria and begin antibiotic treatment as soon as possible.
Bacterial infection in the ears, mouth, or sinuses can spread directly to the brain and spinal cord. Some types of bacteria are transmitted from person to person through secretions from the mouth and nose.
Fungal meningitis develops in patients with conditions that compromise the effectiveness of their immune systems (e.g., HIV/AIDS, lupus, diabetes). Fungal meningitis occurs in 10% of patients with AIDS. Crytococcus neoformans and Candida albicans are commonly involved in fungal meningitis.
Parasitic meningitis is more common in underdeveloped countries and usually is caused by parasites found in contaminated water, food, and soil.
Noninfectious meningitis may develop as a complication of another illness (e.g., mumps, tuberculosis, syphilis). A break in the skin and/or bones in the face or skull (caused by birth defect, brain surgery, head injury) can allow bacteria to enter the body.
Rarely, meningitis can be caused by exposure to certain medications, such as the following:
Incidence and Prevalence
Most (approx. 70%) cases of meningitis occur in children under the age of 5 and people over the age of 60.
In the United States, bacterial meningitis affects about 3 in 100,000 people each year, and viral meningitis affects about 10 in 100,000.
Hib vaccine has reduced U.S. incidence of bacterial meningitis caused by Haemophilus influenzae type b by approximately 90%. The disease is more prevalent in people between the ages of 15 and 24 who have not been vaccinated.
Worldwide, bacterial resistance to penicillin and other antibiotics and the lack of access to vaccines accounts for rising rates of bacterial meningitis.
The primary risk factor for meningitis is a suppressed immune system, which may be caused by the following:
Not receiving the mumps, Haemophilus influenzae type b, and pneumococcal (children aged 2 and younger) vaccines increases the risk for meningitis.
Age is also a risk factor for meningitis. It is more common in people younger than 5 years old and those older than 60. People between the ages of 15 and 24 who live in boarding schools and college dormitories are also at increased risk.
Living and working with large groups of people (e.g., military bases, child care facilities) increases the risk for infectious meningitis.
People who work with domestic animals (e.g., dairy farmers, ranchers) and pregnant women are at increased risk for meningitis associated with listeriosis (disease transmitted from animals to humans via soil). Listeriosis can be transmitted from mother to fetus through the placenta, causing spontaneous abortion. The disease is usually fatal in newborns.
Head injuries and brain surgery also put patients at risk for meningitis.
Viruses and bacteria that spread to or directly infect the central nervous system cause most cases of infectious meningitis.
About 90% of cases of viral meningitis are caused by one of the enteroviruses (e.g., coxsackievirus, echovirus, poliovirus). Mumps, herpesvirus, and arboviruses (transmitted by insect bites) also may cause viral meningitis. About 30% of mumps cases in people not vaccinated for the disease develop meningitis.
Common causes of bacterial meningitis include Streptococcus pneumoniae, Neisseria meningitides, Staphylococcus aureus, Escherichia coli, and Staphylococcus epidermidis. Prior to the 1990s, Haemophilus influenzae type b was the primary cause, but widespread vaccination (Hib vaccine) has greatly reduced the incidence of this infection.
Candida albicans, Crytococcus neoformans, and Histoplasma are often involved in cases of fungal meningitis.
Causes of noninfectious meningitis include the following:
Signs and Symptoms
Symptoms of bacterial meningitis are usually acute, developing within a few hours and last 2 to 3 weeks. It is important to seek immediate medical attention when symptoms occur, because acute bacterial meningitis can be fatal within hours.
Viral meningitis may develop suddenly or within days or weeks, depending on the virus and the overall health of the patient.
Characteristic symptoms of both viral and bacterial meningitis are stiff neck, headache, and fever. Symptoms may develop over the course a few hours (acute bacterial meningitis) or a few days. Some patients experience cough, runny nose, and congestion prior to developing other symptoms.
Other signs and symptoms of meningitis include the following:
Symptoms of meningitis in infants may be difficult to detect and include the following:
Complications such as the following can develop during the course of meningitis:
Prompt medical treatment decreases the risk for brain damage and long-term complications, including these:
Severe bacterial meningitis also may cause the head and heels to bend backward and the body to bow forward (called opisthotonos), coma, and death.
Newborns and young children may develop heart, liver, intestinal problems, or malformed limbs.
A diagnosis of meningitis depends primarily on a thorough physical examination and cerebrospinal fluid (CSF) analysis.
In the physical examination stiff neck, severe headache, and fever indicate meningitis. It may be extremely painful to move the neck forward. The neck may be so stiff that attempting to move it causes the entire body to move. Other signs the physician may look for include swelling in the eyes, which indicates elevated intracranial pressure, and skin rash.
Computed tomography (CT scan) or magnetic resonance imaging (MRI scan) of the brain may be used to evaluate possible swelling (edema) and bleeding (hemorrhage) and to rule out other neurological disorders.
Laboratory tests that may be performed include complete blood count (CBC), blood culture, and spinal tap. CBC will show elevated levels of white blood cells if there is an active infection in the body. Blood is cultured to identify bacteria in the blood.
Spinal tap, or lumbar puncture, is essential in diagnosing and selecting appropriate treatment for meningitis. About 2 tablespoons of cerebrospinal fluid is drawn into a needle inserted between two lumbar vertebrae. Lab analysis looks for elevated levels of white blood cells and blood. The fluid also is cultured to identify the organism causing meningitis.
Treatment is determined by the type of meningitis and the organism causing the disease.
Viral meningitis usually requires only symptom relief (palliative care). Palliative care may include bed rest, increased fluid intake to prevent dehydration, and analgesics (e.g., aspirin, acetaminophen) to reduce fever and relieve body aches.
Meningitis caused by herpesvirus can be treated using antiviral medication such as acyclovir (Zovirax®) or ribavirin (Virazole®). Side effects of these medications include nausea, vomiting, and headache.
Suspected bacterial meningitis requires prompt intravenous (IV) antibiotic treatment in the hospital to prevent serious complications and neurological damage. If symptoms are severe, IV treatment may be initiated before the lumbar puncture is performed.
Severly ill patients are treated immediately with a combination of antibiotics. Penicillin combined with a cephalosporin (e.g., ceftriaxone [Rocephin®], cefotaxime [Claforan®]) is commonly used. Because some bacteria are resistant to these drugs, vancomycin, with or without rifampin, ampicillin, and gentamicin may be added to cover resistant pneumococcal strains of bacteria and Listeria monocytogenes.
Side effects include abdominal pain, nausea, vomiting, and diarrhea. Once the CSF culture has revealed the disease-causing organism (pathogen), antibiotic treatment is adjusted accordingly.
Amphotericin B and fluconazole (Diflucan®) are effective against most disease-causing fungi and are the drugs of choice for treatment of fungal meningitis. They may be administered singly or as combined therapy. Both drugs are well tolerated in most patients.
Possible side effects of fluconazole include nausea and vomiting, diarrhea, headache, skin rash, and abdominal pain. Intravenously administered amphotericin B may produce the same side effects, as well as shaking chills and fever, slowed heart rate, low blood pressure (hypotension), body ache, and weight loss.
Parasitic meningitis usually is treated with a benzimidazole derivative or other antihelminthic agent.
Complications that develop also must be treated. Corticosteroids (e.g., dexamethasone) may be administered to reduce the risk for hearing loss. Increased intracranial pressure may be reduced with diuretics (e.g., mannitol) and a surgically placed shunt that drains excess fluid.
Bacterial meningitis is fatal in as many as 25% of cases. Patients with meningitis caused by Streptococcus pneumoniae and patients younger than 2 years old or over the age of 60 have a poor prognosis. Prompt medical treatment (i.e., antibiotics) reduces the risk for dying from bacterial meningitis to less than 15%.
Viral meningitis usually resolves in 7-10 days and is fatal in fewer than 1% of cases.
Immunization with the vaccines listed below is the most effective way to prevent meningitis:
Medications such as rifampin (Rifadin®), ceftriaxone (Duricef®), and ciprofloxacin (Cipro®) may be used to prevent the development of bacterial meningitis in people exposed to the disease.