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Group B streptococcus: Virulence factors and pathogenic mechanisms

Lawrence C Madoff, MD
Section Editor
Daniel J Sexton, MD
Deputy Editor
Allyson Bloom, MD


Group B streptococcus (GBS; Streptococcus agalactiae) is a gram-positive coccus that frequently colonizes the human genital and gastrointestinal tracts [1,2]. It is an important cause of infection in three populations:

Neonates — GBS infection is acquired in utero by ascending infection or during passage through the vagina. Neonatal disease is categorized by the age at onset into early- and late-onset infection. Early-onset most commonly presents at or within 12 hours of birth but, by definition, can occur through day six of life. The most common manifestations are bacteremia without a focus, sepsis, pneumonia, and/or meningitis. Late-onset infection occurs after day six and up to 90 days of life. It most often presents as bacteremia without a focus (65 percent of cases) but meningitis (32 percent) and focal infections also occur. Late-onset infections most frequently are caused by serotype III GBS. (See "Group B streptococcal infection in neonates and young infants".)

Pregnant women — GBS is a frequent cause of urinary tract infection (usually asymptomatic bacteriuria), chorioamnionitis, postpartum endometritis, and peripartum bacteremia. (See "Group B streptococcal infection in pregnant women".)

Nonpregnant adults — GBS is increasingly recognized as a cause of sepsis, soft tissue infections, and other focal infections in nonpregnant adults. These infections occur predominantly in those with chronic underlying medical conditions, such as diabetes mellitus, malignancy especially breast cancer, and liver disease. However, GBS also can cause infection in healthy patients over the age of 65 years. (See "Group B streptococcal infections in nonpregnant adults".)

The microbiology of GBS will be reviewed here. GBS infection and treatment in neonates and young infants, pregnant women, and nonpregnant adults and prevention strategies through chemoprophylaxis and vaccination are discussed separately. (See "Group B streptococcal infections in nonpregnant adults" and "Group B streptococcal infection in neonates and young infants" and "Group B streptococcal infection in pregnant women" and "Neonatal group B streptococcal disease: Prevention" and "Vaccines for the prevention of group B streptococcal disease".)


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Literature review current through: Sep 2016. | This topic last updated: Jul 6, 2015.
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