Streptococcal Infections, Group B
Streptococcal Infections, Group B
Disease History, Characteristics, and Transmission
Introduction
Group B Streptococcus bacteria, primarily the species Streptococcus agalactiae, are a major cause of sickness and death among newborns worldwide. Group B Streptococcus illnesses are also known as GBS, Beta strep, or group B Streptococci. GBS infection also increases risks to both the mother and the fetus before birth. In the newborn, infection can cause pneumonia (fluid in the lungs) and bacteremia (bacteria in the blood, which is normally sterile) within the first week after birth. The late-onset form of the disease occurs from 7 to 90 days after birth, usually causing meningitis, which is inflammation of the meninges (the tough membranes that surround the brain and spinal cord). Pneumonia, bacteremia, and meningitis can all be fatal. GBS infection can be treated with antibiotics, but no vaccine is currently available.
Disease History, Characteristics, and Transmission
Streptococci, which are Gram-positive bacteria that tend to grow in chains or pairs, were first described in 1874 by Christian Theodor Billroth (1829–1894). Around 1903, Hugo Shottmuller (1867–1936) distinguished between alpha-hemolytic and beta-hemolytic Streptococci. Beta-hemolytic Streptococci—which include almost all group A and many group B Streptococci— are distinguished by their ability to completely break up blood cells when grown in the laboratory, a process called hemolysis (hemo meaning blood, and lysis meaning breakup). Hemolysis creates clear areas around colonies of beta-hemolytic bacteria growing in petri dishes on the substance called blood agar, a jellylike substance derived from seaweed or algae mixed with (usually) sheep blood.
GBS is most often noted for causing pneumonia and meningitis in newborns, with a high fatality rate. GBS is also known to cause infections in adults with preexisting conditions such as breast cancer, cirrhosis of the liver, and diabetes. In adults, GBS can manifest as a soft-tissue infection, pneumonia, meningitis, or infections of the bones or joints. The elderly are at greatest risk from these invasive GBS infections.
GBS is usually transmitted by direct contact. Newborns may contract the bacteria during labor and delivery by mothers who are vaginally or anally colonized with the bacteria. Alternatively, fetuses may contract the bacteria from their mothers during development, before birth. This can lead to miscarriage or premature birth, and approximately triples the risk of cerebral palsy.
Scope and Distribution
Like group A streptococci, GBS are common in human populations. They are particularly important as a cause of infection in newborns, causing several thousand deaths per year in the United States alone. About 12% to 27% of women in North Africa, south-central Asia, Saudi Arabia, and the United States are colonized by GBS.
Treatment and Prevention
Although GBS can be treated with antibiotics, infection can spread quickly and symptoms can be difficult to diagnose in newborns. Administration of antibiotics— usually penicillin or ampicillin—to the mother during delivery can prevent infection in newborns.
Research is under way for the use of monoclonal antibodies as a vaccine for GBS, but, as of early 2007, had not yet reached the stage of clinical trials with human subjects. Strains of GBS causing bacteria can vary significantly in different parts of the world, challenging development of a single GBS vaccine that would be effective worldwide.
WORDS TO KNOW
BACTEREMIA: Bacteremia occurs when bacteria enter the bloodstream. This condition may occur through a wound or infection, or through a surgical procedure or injection. Bacteremia may cause no symptoms and resolve without treatment, or it may produce fever and other symptoms of infection. In some cases, bacteremia leads to septic shock, a potentially life-threatening condition.
COLONIZATION: Colonization is the process of occupation and increase in number of microorganisms at a specific site.
HEMOLYSIS: The destruction of blood cells, an abnormal rate of which may lead to lowered levels of these cells. For example, Hemolytic anemia is caused by destruction of red blood cells at a rate faster than which they can be produced.
MENINGITIS: 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.
MONOCLONAL ANTIBODIES: Antibodies produced from a single cell line that are used in medical testing and, increasingly, in the treatment of some cancers.
Impacts and Issues
In the United States in the 1970s, there were 7,500 GBS infections in newborns per year. The death rate for GBS infection was as high as 50%. In the 1980s, it was found that giving antibiotics to women who tested positive for GBS and were therefore at risk for transmitting the bacteria to their babies greatly reduced the rate of early-onset (first week of life) disease. As a result, the U.S. Centers for Disease Control (CDC) issued guidelines in 1996 recommending vaginal and rectal screening between the 35th and 37th weeks of pregnancy to identify women with GBS; women who test positive are offered antibiotics during labor.
In developing countries, infection rates in newborns are surprisingly low; in a recent study of newborns in India, the Middle East, and elsewhere, only about 1% of newborns tested positive for GBS, even though their mothers were colonized by GBS at a rate of 12% to 27%. It is possible, according to the World Health Organization (WHO), that GBS causes infant death in developing countries primarily by causing miscarriage or premature birth, leading to an artificially low figure for GBS infant mortality.
See AlsoStreptococcal Infections, Group A.
BIBLIOGRAPHY
Periodicals
Osrin, David, et al. “Serious Bacterial Infections in Newborn Infants in Developing Countries.” Pediatric and Neonatal Infections. 17 (2004): 217–224.
Benitz, Willem E., et al. “Risk Factors for Early-onset Group B Streptococcal Sepsis: Estimation of Odds Ratios by Critical Literature Review.” Pediatrics. 103 (1999): 1–14.
Web Sites
Centers for Disease Control and Prevention. “Prevention of Perinatal Group B Streptococcal Disease.” August 16, 2002 <http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5111a1.htm> (accessed February 2, 2007).
Royal College of Obstetricians and Gynaecologists (United Kingdom). “Prevention of Early Onset Neonatal Group B Streptococcal Disease.” November, 2003 <http://www.rcog.org.uk/index.asp?PageID=520> (accessed February 2, 2007).