Correlates of antibiotic-resistant group B streptococcus isolated from pregnant women.

Despite antibiotic prophylaxis for at-risk mothers during labor and delivery, group B streptococcus still causes substantial morbidity and mortality among newborns. Resistance to antibiotics recommended for penicillin-allergic pregnant women, such as erythromycin and clindamycin, has increased. A better understanding of factors associated with group B streptococcus resistance is essential to effectively prevent group B streptococcus disease.A total of 117 sequential group B streptococcus isolates were obtained between August 1999 and March 2000 from pregnant women at the University of Michigan Medical Center. Serotype and susceptibility to ten antimicrobials using disk diffusion with E-test for confirmation were determined, and the association between several host factors and colonization with a resistant strain was evaluated. Group B streptococcus was frequently resistant to erythromycin (29%) and clindamycin (21%) but was susceptible to all other antimicrobials tested. A stepwise logistic regression model revealed that black ethnicity (P =.02) and carriage of a serotype V strain (P =.01) were associated with group B streptococcus resistance. Among this population of pregnant women, black ethnicity and serotype V were the strongest predictors of colonization with an erythromycin- or clindamycin-resistant group B streptococcus strain. A better understanding of factors associated with antibiotic resistance is needed to minimize group B streptococcus disease risks and to maximize effective chemoprophylaxis.