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Medical Author:

Mary Nettleman, MD, MS, MACP

Mary Nettleman, MD, MS, MACP

Mary D. Nettleman, MD, MS, MACP is the Chair of the Department of Medicine at Michigan State University. She is a graduate of Vanderbilt Medical School, and completed her residency in Internal Medicine and a fellowship in Infectious Diseases at Indiana University.

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Medical Editor:

Melissa Conrad Stöppler, MD, Chief Medical Editor

Melissa Conrad Stöppler, MD, Chief Medical Editor

Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

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Group B strep infections are caused by bacteria from the species and genus Streptococcus agalactiae. Streptococci were divided into groups in 1933 by mixing the strains with antibodies that were produced in rabbits. Group B streptococci (GBS) have an outer cell wall that serves as a protective capsule which helps the organism resist the body's attempts to fight off the bacteria.

Group B strep may live harmlessly in the human body, which is called "colonization" or "carriage." During colonization, the organism lives on surfaces and membranes but does not invade tissues or organs. The most common site of colonization for group B strep is in the bowels. Approximately 20%-40% of women are colonized with group B strep in the vagina or cervix. Colonization is more common in people with diabetes and those who are sexually active.

An infection occurs when the bacteria invade the bloodstream, tissues, or organs. Newborns can become infected with group B strep as they pass through the birth canal if the mother carries the organism in her vagina. These infections are early-onset since they appear within the first week of life, often in the first hours after birth. In mothers colonized with group B strep, approximately 1% of newborns will have early-onset infection. Since group B strep is carried in the bowels, the organism may also be spread if a person does not wash their hands properly after using the bathroom. Babies can also be infected this way, usually in the home, causing late-onset infections, which occur when the baby is 1 week to 3 months old.

Group B strep is not a cause of birth defects or autism and is not a sexually transmitted disease. Although babies may contract infections by contact with contaminated hands, washing with simple soap and water eliminates the organism. Group B strep is not contagious through coughing or sneezing.

Group B strep is a cause of infection in pregnant women. The organism may infect the bloodstream or the uterus. Older children and nonpregnant adults, especially older adults in nursing homes, may also get infections with group B strep.

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