Vaginal-perianal compared with vaginal-rectal cultures for identification of group B streptococci

To estimate whether the rates of recovery of group B streptococci from combined vaginal and perianal cultures and combined vaginal and rectal cultures are equivalent.

We performed a prospective cohort study of vaginal-perianal versus vaginal-rectal culture for group B streptococci. Two hundred pregnant women in the third trimester were enrolled. Three specimens were collected from each patient in the following order: lower third of the vagina, perianal skin, and rectum. Each specimen was cultured serially in selective broth media, then on sheep's blood agar. Suspicious colonies were confirmed by latex agglutination. Culture positivity rates from the combined sites of vagina and perianal skin were compared with vagina and rectum. Laboratory personnel were blinded to the collection site of each individual swab.

Of the 200 subjects, 71 (36%) had a positive culture from at least 1 site. Vaginal culture was positive in 55 patients (28%), compared with 48 patients (24%) with positive perianal cultures and 50 patients (25%) with positive rectal cultures. Results of combined vaginal and perianal cultures were positive in 68 patients (34%); results of combined vaginal and rectal cultures were positive in 67 patients (34%) (P = 1.0).

The group B streptococci detection rate from vaginal-perianal specimens is not significantly different from the detection rate from vaginal-rectal specimens. Therefore, pregnant women do not need to be subjected to the discomfort of collection of a rectal specimen.

II-2.