The objective of this study was to evaluate the rates of clindamycin and erythromycin resistance among group B Streptococcus (GBS)-positive isolates cultured from pregnant women in an upstate New York community hospital. All GBS-positive perinatal rectovaginal cultures obtained from January 2010 through October 2011 were tested for resistance to erythromycin and clindamycin. Among the 688 GBS-positive cultures, clindamycin resistance was found in 38.4% and erythromycin resistance was found in 50.7%. Rates of GBS resistance to clindamycin and erythromycin are much higher than reported in earlier U.S. studies, suggesting both increasing resistance and regional variation in resistance. These findings lend strong support to the CDC and American College of Obstetricians and Gynecologists (ACOG) recommendations that clindamycin use for intrapartum antibiotic prophylaxis be restricted to penicillin-allergic women at high risk of anaphylaxis and that GBS isolates be tested for antibiotic resistance prior to the use of clindamycin in these women. Routine screening for maternal colonization by group B Streptococcus (GBS) and intrapartum treatment of infected mothers have been a significant public health success. According to the Centers for Disease Control and Prevention (CDC), the incidence of neonatal GBS infection, a major cause of morbidity and mortality, has declined dramatically over the past 15 years, from 1.7 cases per 1,000 live births in the early 1990s to 0.34 to 0.37 cases per 1,000 live births in recent years. The most recent perinatal GBS guidelines issued by the CDC in November 2010 uphold previous antibiotic recommendations for the prophylactic treatment of GBS-colonized women during labor, except for the withdrawal of erythromycin as a second-line prophylactic antibiotic for women with penicillin allergy (6). These recommendations have also been endorsed by the American Congress of Obstetricians and Gynecologists (ACOG) in their recent committee opinion issued in April 2011 (1). According to the CDC and ACOG recommendations, clindamycin is still an acceptable alternative for women with penicillin allergy, provided that the GBS isolates have been tested for clindamycin susceptibility (1, 6). Although intrapartum antibiotic prophylactic (IAP) treatment with penicillin and ampicillin has been shown to prevent early-onset GBS disease in clinical trials, concerns have been raised regarding the ability of clindamycin, erythromycin, and vancomycin to reliably reach bactericidal levels in the amniotic fluid, fetal circulation, and fetal tissues. Additionally, according to the CDC guideline report, in vitro resistance to both clindamycin and erythromycin has been increasing, with reports published from 2006 to 2009 finding GBS resistance ranging from 25% to 32% for erythromycin and from 13% to 20% for clindamycin (6).In May 2009, Ellis Hospital, the only hospital with maternity services in Schenectady, NY, initiated testing of all GBS isolates for resistance to both erythromycin and clindamycin. This initiative wa...