Bacterial meningitis refers to an acute disease caused by several different types of bacteria, in which a membrane called the meninges, which surrounds the brain and the spinal cord, becomes inflamed. Inflammation-related swelling of the membrane can cause serious problems that include septicemia (blood poisoning) brain damage, coma, and death.
Bacterial meningitis is the result of a bacterial infection of the blood that spreads to the cerebrospinal fluid, which is the fluid that flows around the meninges. The illness is serious; if not treated, the death rate is high. Those who survive can be left with life-long disabilities that includes impaired hearing due to damage to the hair cells in a portion of the ear that are responsible for converting sound waves to the electrical signals that the brain can interpret. Longer-term problems also include paralysis, mental dysfunction, and paralysis.
Like other bacterial diseases such as plague and anthrax, bacterial meningitis has likely been occurring for thousands of years. Comparison of the genetic material of the bacteria that cause meningitis with other bacteria—an approach that can indicate whether the bacteria have existed for a long time or have appeared relatively recently—indicates that bacterial meningitis is ancient in its origin. Documented descriptions of the disease date back to 1805, when an outbreak was described in Geneva, Switzerland. In that century, meningitis also decimated the ruling family in Japan.
Bacterial meningitis can be caused by a number of different strains of bacteria. The bacteria that are the most common causes are Neisseria meningitidis (also known as meningococcus), Streptococcus pneumoniae (also known as pneumococcus), and Listeria monocytogenes. Less commonly, Pseudomonas aeruginosa, Staphylococcus aureus, Streptococcus agalactiae, and Haemophilus influenzae type b (also known as Hib) can cause meningitis. As well, Mycobacterium tuberculosis can be a problem in developing countries.
The less common bacteria are often not a health concern. But, in someone whose immune system is inefficiently functioning due to age, illness, or deliberate immunosuppression (as occurs following organ transplantation to avoid rejection of the transplant) the bacteria are capable of causing meningitis infection.
The source of the infection is sometimes never determined. It is known that bacteria can spread from an ear infection to the meninges. The most common source is the spread of bacteria into the bloodstream from an infection in the heart (endocarditis). In endocarditis, the infecting bacteria can adhere to tissues and produce a colony of bacteria that is enclosed in a slimelike overlay. The organized structure, which is called a biofilm, can then slough off bacteria into the bloodstream.
Infection of the meninges by bacteria usually produces a fever, headache, sensitivity to light, and mental disorientation. As well, when the spinal cord is involved, a person can experience pain in the neck and the legs that becomes progressively worse. These symptoms also occur in the type of meningitis that is caused by viruses. Distinction between the two types of meningitis usually requires obtaining the bacteria from the cerebrospinal fluid. The bacteria are detected when the cerebrospinal fluid is added to a culture, source of nutrients that the bacteria can use. With time, the bacteria grow and divide repeatedly to form a visible mound of cells called a colony.
Bacteria can also be detected by a staining procedure called the Gram stain. Depending on which of two stains the bacteria retain, they can be distinguished as Grampositive (these bacteria have a single membrane) or Gramnegative (which have two membranes). This distinction is important for determining the most effective antibiotic to use. Streptococcus pneumoniae is an example of a Gram-positive bacterium that can cause meningitis. Neisseria meningitidis is an example of a Gram-negative bacterium that is a cause of meningitis.
In the meningitis due to Neisseria meningitidis, the first symptoms to appear is often a rash that appears as small reddish or purple spots. The rash can spread quickly over the middle part of the body, legs, the conjunctiva in the eyes, and parts of the hands and feet.
Bacterial meningitis occurs all over the world. In areas such as Sub-Saharan Africa, the disease is especially prevalent.
The main reason for the global distribution of bacterial meningitis is the equally wide distribution of the bacteria. Some of the bacteria capable of causing meningitis are normally found in the mouth. These can be spread from person to person by coughing or kissing.
In developed countries including the United States, meningitis is rare and occurs as isolated cases. More widespread epidemics still do occur in other parts of the world, in particular northern Africa.
Bacterial meningitis is treated with antibiotics. The choice of the antibiotic depends on the bacterium that is causing the infection. But, when first treating an infection that is suspected of being meningitis, several antibiotics that are effective against the widest variety of bacteria are often used even before the cause of the infection has been identified. This is done because rapid treatment is important to minimizing the danger of the infection. Once the cause of the infection has been determined, the antibiotic therapy can be adjusted to specifically target the particular bacterium.
WORDS TO KNOW
BIOFILM: Biofilms are populations of microorganisms that form following the adhesion of bacteria, algae, yeast, or fungi to a surface. These surface growths can be found in natural settings such as on rocks in streams, and in infections such as can occur on catheters. Microorganisms can colonize living and inert natural and synthetic surfaces.
MENINGITIS BELT: The Meningitis Belt is an area of Africa south of the Sahara Desert, stretching from the Atlantic to the Pacific coast, where meningococcal meningitis is common.
SEPTICEMIA: Prolonged fever, chills, anorexia, and anemia in conjunction with tissue lesions.
STRAIN: A subclass or a specific genetic variation of an organism.
ASEPTIC AND BACTERIAL MENINGITIS
The meninges are a series of three membranes covering the brain and spinal cord that act to protect and partition the central nervous system (CNS). The membranes comprising the meninges are the dura mater, arachnoid layer, and the pia mater.
Meningitis is an inflammation of the meninges—the three layers of protective membranes that line the spinal cord and the brain. Meningitis can occur when there is an infection near the brain or spinal cord, such as a respiratory infection in the sinuses, the mastoids, or the cavities around the ear. Disease organisms can also travel to the meninges through the bloodstream. The first signs may be a severe headache and neck stiffness followed by fever, vomiting, a rash, and, then, convulsions leading to loss of consciousness.
Meningitis generally involves two types: non-bacterial meningitis, which is often called aseptic meningitis, and bacterial meningitis, which is referred to as purulent meningitis.
Antibiotics are usually given intravenously—they are added directly into a vein, where they circulate in the bloodstream. This produces a high level of the antibiotic throughout the body and, because the antibiotic can be continuously supplied, the dose can stay constant during the several weeks of treatment that is usually required.
Vaccines directed towards Neisseria and Haemophilus have lessened childhood meningitis dramatically. Two Neisseria meningitidis vaccines are available in the United States. One has been available since the early 1980s, while the other was approved only in 2005. As well, both newborns and the elderly benefit from vaccines against Streptococcus pneumoniae. The American Association of Pediatrics recommends vaccinating newborns against penumococcal meningitis as early as six weeks after birth and the U.S. Centers for Disease Control and Prevention recommends vaccination for everyone over the age of 65.
Bacterial meningitis continues to be a great health concern, especially in some under-developed regions of the world. In areas of Sub-Saharan Africa known as the meningitis belt, epidemics of meningitis continue to kill many people. In 1996, more than 250,000 contracted meningitis during one epidemic, and about 25,000 people died of the disease. While outbreaks that large are not common, the occurrence of the disease is a frequent occurrence in some areas of their world.
This continued threat posed by bacterial meningitis is one of the health concerns being addressed by the World Health Organization as part of the Consolidated Appeals Process, which seeks to galvanize support from countries around the globe to assist in aiding underdeveloped regions.
In both under-developed and developed countries, the disease is a serious health concern for infants less than a year old; the high fever that can be produced can cause seizures. Because bacterial meningitis is contagious, infants in day care facilities are at increased risk for the disease.
Despite the ongoing problem of bacterial meningitis, the introduction of vaccines has greatly reduced the prevalence of the infection. Before a vaccine to Haemophilus influenzae type b was introduced in the 1990s, meningitis due to Hib was the leading cause of bacterial meningitis. Now, because of the routine immunization of schoolchildren with a Haemophilus vaccine, Hib meningitis is rare.
For survivors of a bacterial meningitis infection, hearing loss can be a consequence. Artificial implants in an area of the ear called the cochlea can sometimes restore hearing to a level that allows normal function. But, the implant must be installed within weeks of the end of an infection to be fully effective. This is because the fluid that has accumulated in the ear changes consistency over time and becomes almost jellylike, making installation of an implant impossible.
Ferreiros, C. Emerging Strategies in the Fight Against Meningitis. Oxford: Garland Science, 2002.
Lax, Alister. Toxin: The Cunning of Bacterial Poisons. Oxford: Oxford University Press, 2005.
Wilson-Clark, Samantha D., S. Squires, S. Deeksi “Bacterial Meningitis among Cochlear Implant Recipients—Canada 2002.” Morbidity and Mortality Weekly. 55: S20-S25 (2006).
Centers for Disease Control and Prevention. “Meningococcal Disease” <http://www.cdc.gov/ncidod/dbmd/diseaseinfo/meningococcal_g.htm> (accessed May 25, 2007).
World health Organization. “Meningitis in Africa: Hundreds of Thousands Vaccinated.” <http://www.who.int/mediacentre/news/notes/2007/np12/en/index.html> (accessed May 25, 2007).