Maternal group b streptococcal (GBS) culture status of infants GBS positive at delivery

Objectives: The purpose of the study was to evaluate maternal determinants of infant Group B Streptococci colonization at delivery. Study Design: A cohort of 536 mother/infant pairs were enrolled at Magee-Womens Hospital from July 1995 to February 1996. Infants had specimens taken before 12 hr of life for the isolation of GBS from the outer ear, throat, anus, and umbilicus. Specimens were grown on solid media following broth enrichment. Medical records were reviewed to determine the mother's antepartum (AP) GBS culture and intrapartum (FP) chemoprophylaxis status. A subgroup of 216 mothers also had IP vaginal specimens taken for GBS isolation when they were admitted for delivery. Results: Maternal GBS colonization rates in the AP and IP were 26% and 24%, respectively. Seven percent (38/536) of infants were GBS positive from at least one site. Infants were more likely to be positive if maternal AP cultures had been positive (12% versus 5%; P=0.02) but 56% of positive infants were born to culture negative mothers Infants treated with IP antimicrobials for > 4 hr had a 54% reduction in colonization (95% CI 0.2-L3) compared to infants whose mothers were untreated or treated <4 hr AP cultures were 77% sensitive and 82% specific for predicting women positive at delivery but 23% of women who were positive at delivery were negative earlier in pregnancy. Women who were positive at any testing time were more likely to have a culture positive infant when compared to those who were negative at both testing times (19% versus 0.7%; P < 0.0001). Conclusions: Antepartum maternal specimens taken for the isolation of GBS are inadequate predictors of which women will be positive at delivery. Negative antepartum maternal culture sta:us may result in false reassurance that the infant is not at risk for invasive GBS disease.