Group B Strep (Strepococcus agalactiae, group B) is a common bacteria. In older children and adults, colonization of the bacteria rarely results in infection. That means one may carry the bacteria, but never show signs of disease. In fact, as many as 10-30% of the female population are carriers of the bacteria. The bacteria can be detected by a culture of the vagina and rectum.
Though uncommon, if some newborns become infected, the results can be devastating. But even in women known to carry the bacteria, infection of the newborn is rare (about 1%). Overall, in the pregnant population, the risk of newborn infections is only 2 or 3 per 1,000 births.
Many of the most severe newborn GBS infections occur in babies born prematurely. Their immune systems are not fully developed, and cannot fight off infection very well. Also, in the past, because of its rarity, the infection was often not diagnosed early enough, and this contributed to many of the poor outcomes. Fortunately, in newborns, prompt treatment with common antibiotics (penicillin) is highly effective in preventing serious problems.
During the 1980’s and 90’s, several research projects attempted to guide clinicians about how best to screen for and treat the potential problem. For a period, all women were screened with vaginal and rectal cultures during pregnancy and treated with antibiotics if they carried the bacteria. This resulted in about 100 women being treated for every 1 baby at risk. And often, the bacteria reappeared in the women soon after treatment.
In 2002, the U.S. Centers for Disease Control recommended that all pregnant women be screened for GBS with a culture of the genital track and anus. If a woman is a carrier for GBS she should be given antibiotics when she is in labor. Treating during pregnancy is often ineffective since it is very difficult to kill ALL the bacteria on an adult body. However, treating the mother during labor assures the baby is well-protected.
Treatment during labor usually consists of intravenous antibiotic therapy. The drug of choice is penicillin, or, for those allergic to penicillin, clindamycin or any other strep-specific antibiotic.