Rectal colonization by group B Streptococcus as a predictor of vaginal colonization.

Objective: The purpose of this article was to describe rectal colonization by group B Streptococcus (GBS) and its role in the prediction of vaginal colonization.

Methods: In this prospective cohort of 1248 nonpregnant women, vaginal and rectal swabs for GBS culture were obtained at enrollment and at three 4-month intervals. Generalized estimating equations were used to identify factors that are associated with colonization.

Results: Eight hundred fourteen (65%) women had GBS colonization sometime during the observation period. Rectal GBS colonization was the strongest predictor of vaginal colonization (adjusted odds ratio, 14.3; 95% CI, 11.9-17.1). Recent sexual intercourse, vaginal colonization with yeast, and a vaginal Nugent score >/= 4 were also independent determinants of vaginal GBS colonization. Antimicrobial use decreased vaginal GBS colonization only among women who had no rectal colonization.

Conclusions: GBS in the gastrointestinal tract is a risk factor for vaginal GBS. Sexual activity and abnormal vaginal microflora are independent determinants of vaginal GBS colonization.