The effect of intrapartum clindamycin on vaginal group B streptococcus colony counts

Abstract

Objective: To determine the temporal relationship between intrapartum clindamycin and vaginal Group B Streptococcus (GBS) colony counts. Methods: In this prospective observational study, women with GBS-positive, clindamycin-sensitive, antenatal rectovaginal cultures, intrapartum vaginal cultures were collected just before the first clindamycin dose (T0) and then every 2 h for 8 h or until delivery. Colony counts were quantified using serial dilution. Results were standardized as percent of initial colony count and analyzed using sequential Friedman tests. Results: Twenty-one women had positive intrapartum vaginal GBS cultures at T0. With T0 colony counts standardized to 100%, subsequent percents-of-baseline fell rapidly and significantly by T2 and fell further at each subsequent point, reaching 0% by T6. For 12 women cultured for the full 8 hours, the decline in GBS was significant at p < 0.001. Conclusions: Vaginal GBS colony counts fall rapidly after intrapartum clindamycin administration, similar to declines after penicillin. This represents a possible mechanism for efficacy of chemoprophylaxis.