Antibiotics sharply reduce vaginal GBS

Vaginal group B streptococcus (GBS) colony counts fall quickly and dramatically with intrapartum doses of penicillin-G, researchers report in the December issue of the American Journal of Obstetrics and Gynecology.

Anna R. McNanley, MD, of the University of Rochester Medical Center in Rochester, NY, and colleagues obtained and analyzed vaginal cultures from 50 women in labor who had tested positive for GBS. Beginning just before the initial intravenous antibiotic administration, vaginal cultures were collected every 2 hours up to four times or until delivery, whichever came first.

Thirty-five of the 50 women (70%) had positive intrapartum vaginal cultures, of which 27 received intrapartum penicillin-G. The researchers found that the mean vaginal GBS counts of women receiving the antibiotic declined fivefold in the first 2 hours of treatment and fiftyfold by 4 hours. By 6 hours, mean GBS counts had declined nearly 1,000-fold. They remained at that level at the 8-hour conclusion of the study period.