Anorectal and vaginal carriage of group B streptococci during pregnancy.

A longitudinal prospective study of carriage of group B streptococci during pregnancy was conducted in 2,540 women over a three-year period. Carriage was documented in 18% of the women by anorectal culture, in 4% by vaginal culture, and in 13% by simultaneously obtained anorectal and vaginal cultures (overall carriage rate, 35%). The rate and pattern of carriage were nearly identical from year to year. In sequential cultures in the second and third trimesters of 754 women, carriage rates were 31% and 28%, respectively; only 17% of the women were carriers in both trimesters. (1) Persistence of carriage was most common when the initial anorectal swabs were positive, (2) spread from the intestinal tract to the vagina occurred, and (3) the intestinal tract was commonly the primary site of acquisition in patients with previously negative cultures. The intestinal tract appears to be a primary reservoir for group B streptococci and the likely source of vaginal or urogenital colonization in pregnant women.