Effectiveness of intrapartum antibiotic prophylaxis for prevention of early-onset group B streptococcal disease.

To estimate the effectiveness against early-onset group B streptococcal (GBS) disease of intrapartum antibiotic prophylaxis among term and preterm deliveries, deliveries with fewer than 4 hours of antibiotics, and deliveries receiving clindamycin regimens. We performed a secondary analysis of the Birthnet cohort, a survey of 7,691 births to residents of the Active Bacterial Core surveillance system from 2003 to 2004. We used propensity score matching on covariates associated with prophylaxis and early-onset GBS disease to evaluate the effectiveness (1-risk ratio) of specific intrapartum antibiotic prophylaxis regimens against the disease end point. The effectiveness of 4 or more hours of prophylaxis with penicillin or ampicillin was high among term (91%, 95% confidence interval [CI] +63% to +98%) and preterm (86%, 95% CI +38% to +97%) neonates. Effectiveness was significantly lower for clindamycin (22%, 95% CI -53% to +60%). The effectiveness of 2 or fewer to fewer than 4 hours of prophylaxis with penicillin or ampicillin before delivery (47%, 95% CI -16% to +76%) and the effectiveness of prophylaxis with penicillin or ampicillin fewer than 2 hours before delivery (38%, 95% CI -17% to +67%) were both lower than the effectiveness of prophylaxis durations at 4 or more hours. Beta-lactam prophylaxis given 4 or more hours before delivery is highly effective for prevention of early-onset GBS disease. Prophylaxis of shorter durations or with clindamycin is less effective, reinforcing the need for health care providers to adhere to prevention recommendations, particularly for preterm deliveries, penicillin-allergic women, and neonates exposed to fewer than 4 hours of prophylaxis.