Laboratory Testing for Group B Streptococcus in the Pregnant Patient

Abstract

Streptococcus agalactiae (group B streptococcus [GBS]), colonizes the vagina and rectum in 25–30% of pregnant women (1–5). GBS infection can cause septic abortion, premature rupture of amniotic membranes, chorioamnionitis, postpartum endometritis, neonatal pneumonia, meningitis, and sepsis. The gastrointestinal tract, in particular the rectum, serves as the natural reservoir for GBS and is the likely source of vaginal colonization via transperitoneal contamination. Once in the vagina, the bacterium can be transferred between a woman and man during sexual intercourse, but it should not be classified as a venereal disease because the bacterium appears to wax and wane among the endogenous vaginal microflora. A unique characteristic of vaginal colonization is its resistance to oral, intramuscular, and intravenous antibiotics. However, the administration of intravenous antibiotics during labor does have the ability to prevent neonatal colonization and infection. The benefit of intrapartum antibiotic prophylaxis is to suppress the growth of GBS and colonization of the upper genital tract (i.e., uterine contents) during labor.