Group B Strep (cont.)

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What causes group B strep infection?

Group B strep can normally be found in 15%-45% of all healthy adult women. It can commonly be found in the intestine, vagina, and rectal area. Most women who are carriers of the bacteria (colonized) will not have any symptoms; however, under certain circumstances, infection of both the mother and/or the newborn can develop. In newborns, if the group B strep infection develops in the first week of life, it is termed early-onset disease. If the group B strep infection develops from 1 week to 3 months of age, it is referred to as late-onset disease. Approximately 1,200 babies in the United States develop early-onset disease each year, with similar rates for late-onset disease.

How is group B strep transmitted?

In newborns, GBS infection is acquired through direct contact with the bacteria while in the uterus or during delivery; thus the infection is transmitted from the colonized mother to her newborn, with a transmission rate of approximately 50% in babies delivered vaginally. However, not every baby born to a colonized mother will develop GBS infection. Statistics show that about one of every 100-200 babies born to a GBS-colonized mother will go on to develop GBS infection.

Group B strep infection is more common in African Americans than in whites. There are also maternal risk factors that increase the chance of transmitting group B strep to the newborn:

  • Labor or membrane rupture before 37 weeks gestation


  • Membrane rupture more than 18 hours before delivery


  • Urinary tract infection with GBS during pregnancy


  • Previous baby with GBS infection


  • Fever during labor


  • Positive culture for GBS colonization at 35-37 weeks

Group B strep infection is not a sexually transmitted disease (STD).

Reviewed by Melissa Conrad Stöppler, MD on 6/30/2011

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