Acute bacterial meningitis is rapidly developing inflammation of the layers of tissue that cover the brain and spinal cord (meninges) and of the fluid-filled space between the meninges (subarachnoid space) when it is caused by bacteria.
The subarachnoid space is located between the middle layer and the inner layer of the meninges, which cover the brain and spinal cord (see Fig. 1: Viewing the Brain). This space contains the cerebrospinal fluid.
When bacteria invade the subarachnoid space, the immune system eventually reacts to the invaders, and immune cells gather to defend the body against them. The result is inflammation—meningitis—which can cause complications such as the following:
Different species of bacteria can cause meningitis. The bacteria most likely to be the cause depends on
Acute bacterial meningitis can develop in infants and children, particularly in geographic areas where children are not vaccinated. As people age, acute bacterial meningitis becomes more common.
In newborns and young infants, the most common causes of bacterial meningitis are
If meningitis develops within the first 48 hours after birth, it is usually acquired from the mother. It may be transmitted from mother to newborn as the newborn passes through the birth canal. In these cases, meningitis is often part of a serious bloodstream infection (sepsis).
In older infants, children, and young adults, the most common causes are
Neisseria meningitidis occasionally causes a rapid, severe infection called meningococcal meningitis, resulting in coma and death within hours. This infection commonly occurs when bacteria from an upper respiratory infection enter the bloodstream. Meningococcal meningitis is highly contagious. Small epidemics of meningococcal meningitis may occur among people living in close quarters, as occurs in military barracks and college dormitories. Neisseria meningitidis becomes less common as people age.
Haemophilus influenzae type B is now a rare cause of meningitis in the United States and Western Europe because most children are vaccinated against this bacteria. However, in areas where the vaccine is not widely used, these bacteria are a common cause, particularly in children aged 2 months to 6 years.
In middle-aged and older adults, the most common cause is
As people age, the immune system weakens, increasing their risk of meningitis due to other bacteria, such as Listeria monocytogenes, E. coli, or other gram-negative bacteria.
Staphylococcus aureus occasionally causes severe meningitis in people of all ages.
Bacterial meningitis can be acquired in different ways, including
Having any of the above conditions increases the risk of developing bacterial meningitis.
Strength of the immune system:
Which bacteria are likely to cause meningitis depends on whether the immune system is normal or weakened. Conditions that can weaken the immune system increase the risk of developing bacterial meningitis. Such conditions include
Which bacteria are likely to cause meningitis also depends on what is weakening the immune system and which part of the immune system is weakened. For example, if people have AIDS or Hodgkin lymphoma, meningitis is more likely to be due to Listeria monocytogenes or the bacteria that cause tuberculosis. In people who have problems producing antibodies (which help the body fight infection) or have had their spleen removed, Streptococcus pneumoniae or, less often, Neisseria meningitidis may cause a rapid, severe form of meningitis. If people have recently had chemotherapy for cancer, meningitis is more likely to be due to Pseudomonas aeruginosa or gram-negative bacteria such as E. coli.
In very young infants (particularly premature infants) and older people, certain parts of the immune system may be weak, increasing the risk of meningitis due to Listeria monocytogenes.
Symptoms vary by age.
In newborns and infants, early symptoms most often include
Unlike older people, most newborns and infants do not have a stiff neck. If meningitis becomes severe, the soft spots between skull bones (called fontanelles), which are present in infants before their skull bones grow together, may bulge because pressure within the skull is increased.
In most children and adults, acute bacterial meningitis begins with symptoms that slowly worsen for 3 to 5 days. These symptoms may include a general feeling of illness, fever, irritability, and vomiting. Some people have a sore throat, cough, and a runny nose. These vague symptoms may resemble those of a viral infection. Early symptoms that suggest meningitis specifically include
The stiff neck due to meningitis is more than just sore. Trying to lower the chin to the chest causes pain and may be impossible. Moving the head in other directions is not as difficult. However, some people do not have a stiff neck, and some have back pain.
Some people have symptoms of a stroke, including paralysis. Some have seizures.
As infection progresses, children and adults can become increasingly irritable, confused, and then drowsy. They may then become unresponsive and require vigorous, physical stimulation to be aroused. This mental state is called stupor. Adults may become seriously ill within 24 hours, and children even sooner. Meningitis may cause coma and death within hours. Bacterial meningitis is one of the few disorders in which a previously healthy young person may go to sleep with mild symptoms and never awaken. In older children and adults, such a rapid death often results from swelling of the brain.
In meningococcal meningitis, the bloodstream and many other organs are often infected. The bloodstream infection (called meningococcemia) can become severe within hours. As a result, areas of tissue may die, and bleeding may occur under the skin, causing a reddish purple rash of tiny dots or larger splotches. Bleeding can occur in the digestive tract and other organs. People may vomit blood, or stool may appear bloody or tarry black. Without treatment, blood pressure drops, leading to shock and death. Typically, bleeding occurs in the adrenal glands, which shut down, making shock worse. This disorder, called Waterhouse-Friderichsen syndrome, is often fatal unless treated promptly.
In some situations, symptoms of bacterial meningitis are much milder than normal, making the disorder more difficult for doctors to recognize. Symptoms are milder when people are being treated with antibiotics for another reason. For example, they may be being treated for another infection (such as an ear or throat infection) when meningitis develops, or early meningitis may be mistaken for another infection and be treated with antibiotics. Symptoms can also be milder in people with a weakened immune system, in alcoholics, and in very old people. In the very old, the only symptom may be confusion.
If bacterial meningitis develops after surgery on the brain or spinal cord, symptoms often take days to develop.
If a child 2 years old or younger has a fever and a parent senses that the child is inexplicably irritable or sleepy, the parent should see or call a doctor immediately, particularly if symptoms do not resolve after an adequate dose of acetaminophen.
Children require immediate medical attention, usually in an emergency department, if they do any of the following:
Adults require immediate medical attention if they have any of the following:
During the physical examination, doctors look for telltale signs of meningitis, particularly a stiff neck. They also look for a rash, especially in children, adolescents, and young adults, and for other symptoms, which may suggest a cause. Doctors may strongly suspect bacterial meningitis based on symptoms and results of the examination, but tests are needed to confirm the diagnosis and to identify the specific bacteria causing it. As soon as doctors suspect bacterial meningitis, they first take a sample of blood for analysis and usually do a spinal tap (lumbar puncture). Then they start treatment with antibiotics immediately, without waiting for test results, because meningitis can progress rapidly.
If it seems safe, doctors do a spinal tap (see Fig. 2: How a Spinal Tap Is Done). However, if they suspect that pressure within the skull is greatly increased (for example, by an abscess, tumor, or another mass in the brain), computed tomography (CT) or magnetic resonance imaging (MRI) may be done first to check for such masses. Doing a spinal tap when pressure within the skull is increased may be dangerous. Parts of the brain may shift downward. If these parts are pressed through the small openings in the tissues that separate the brain into compartments, a life-threatening disorder called brain herniation results (see Sidebar 1: Herniation: The Brain Under Pressure).
During a spinal tap, a thin needle is inserted between two bones (vertebrae) in the lower spine to withdraw cerebrospinal fluid. Doctors look closely at the fluid, which is normally clear but may be cloudy in people with meningitis. Pressure in the subarachnoid space is measured as the cerebrospinal fluid is withdrawn. Pressure is usually high in meningitis. The fluid is then sent to a laboratory to be analyzed. Sugar and protein levels and the number and type of white blood cells in the fluid are determined. This information helps doctors diagnose meningitis and distinguish between bacterial and viral meningitis. The fluid is examined under a microscope to check for and identify bacteria. Other tests may be used to rapidly identify certain bacteria, such as Neisseria meningitidis and Streptococcus pneumoniae. Some of these tests identify specific bacteria by detecting specific proteins (antigens) on the surface of the bacteria. The polymerase chain reaction (PCR) technique, which produces many copies of a gene, may be used to identify the bacteria's unique DNA sequence. However, these tests are not always available. The cerebrospinal fluid is also cultured (to make bacteria grow). Culture helps doctors determine whether bacteria are present and, if so, which bacteria are present and which antibiotics may be most effective. Culture results usually take 24 hours or more. If culture or other tests detect bacteria in cerebrospinal fluid, bacterial meningitis is confirmed.
Until the cause of meningitis is confirmed, other tests using samples of cerebrospinal fluid or blood may be done to check for viruses, fungi, cancer cells, and other substances that routine tests do not identify. Testing for herpes simplex virus, which can infect the brain (causing encephalitis), is particularly important.
Doctors also take samples of blood, urine, and mucus from the nose and throat. In people who have a rash, they may use a small needle to remove fluid and tissue from under the skin where the rash is. These samples are cultured and examined under the microscope to see whether bacteria are present.
Because acute bacterial meningitis can lead to permanent brain or nerve damage or death within hours, treatment is started as soon as possible, without waiting for the results of diagnostic tests and often before a spinal tap is done. At this point, doctors do not know the specific bacteria involved and thus cannot know which antibiotics are most effective. So they choose antibiotics that are effective against the bacteria most likely to be causing the infection, and they usually use two or more antibiotics that are effective against many bacteria. The antibiotics are given intravenously. Also, because inflammation of the brain (encephalitis) due to a herpesvirus may resemble bacterial meningitis, an antiviral drug that is effective against this virus is often given. Once the infecting organism, usually a specific species of bacteria, is identified and tested, the antibiotics are changed to ones that are most effective against that organism, and any unnecessary antibiotics and antiviral drugs are stopped.
Dexamethasone (a corticosteroid) is given to control swelling in the brain. It is given 15 minutes before or at the same time as the first antibiotic dose because swelling can worsen as antibiotics break up the bacteria. Dexamethasone is continued for 2 to 4 days. Dexamethasone can also reduce pressure within the skull. If the adrenal glands are damaged, dexamethasone or another corticosteroid can replace the corticosteroids normally produced by these glands.
Other infections, which may have caused or be caused by meningitis, also require treatment. The infections include sepsis, pneumonia, and a heart infection called bacterial endocarditis.
Fluids lost because of fever, sweating, vomiting, and poor appetite are replaced, usually given by vein (intravenously). Because bacterial meningitis often affects many organs and causes serious complications, people are usually admitted to the intensive care unit.
Complications may require specific treatment.
If treated early, most people recover well. But when treatment is delayed, permanent brain or nerve damage or death is more likely, especially in very young children and people over 60. In some people, seizures that result from meningitis require lifelong treatment. People may have problems such as permanent mental impairment, problems with memory or concentration, learning disabilities, behavioral problems, paralysis, double vision, and partial or complete loss of hearing.
People with acute bacterial meningitis (particularly meningococcal meningitis) are usually placed in isolation until the infection is controlled and they can no longer spread the infection, usually for about 24 hours.
Vaccines for several forms of meningitis are available.
A vaccine can help prevent this type of meningitis. It is given to the following people:
The vaccine is also used when an epidemic occurs or when there is a threat of an epidemic in a group of people living together in close quarters (such as those living in military barracks).
Family members, medical personnel, and others in close contact with people who have meningococcal meningitis should be given an antibiotic (such as rifampin or ciprofloxacin taken by mouth or ceftriaxone given by injection) as a preventive measure.
Meningitis due to Streptococcus pneumoniae:
A vaccine that helps protect against this infection is now routinely given to children.
Meningitis due to Haemophilus influenzae:
Children are now routinely immunized with Haemophilus influenzae type b vaccine. In developed countries, this vaccine has virtually eliminated what once was the most common cause of meningitis in children.
Last full review/revision February 2013 by John E. Greenlee, MD