The outpatient institutional antibiogram does not accurately reflect the susceptibility of prepartum group B streptococcal isolates to erythromycin and clindamycin.

This study compared the antimicrobial susceptibilities of 100 nonduplicate group B streptococcal (GBS) isolates from screening cultures of women attending OB-GYN clinics to a similar number of outpatient infection isolates recorded on the institutional antibiogram of a university teaching hospital. The screening GBS isolates were significantly more susceptible to erythromycin (72% versus 45%) and clindamycin (77% versus 48%) than the infection isolates.