The effectiveness of risk-based intrapartum chemoprophylaxis for the prevention of early-onset neonatal group B streptococcal disease

OBJECTIVE: Our purpose was to evaluate the effectiveness of a risk-based in trapartum antibiotic prophylaxis strategy for the prevention of early-onset neonatal group B streptococcal disease. STUDY DESIGN: Cases and controls were selected from infants born to women w ith one or more risk factors: preterm labor or rupture of membranes, prolon ged rupture of membranes (>18 hours), fever during labor, or previous child with group B streptococcal disease. Cases were matched with controls by bi rth hospital and gestational age. Data abstracted from medical records were analyzed to estimate the effectiveness of intrapartum antibiotic prophylax is. RESULTS: We analyzed data from 109 cases and 207 controls. Nineteen (17%) c ase Versus 69 (33%) control mothers received an acceptable regimen of intra partum antibiotic prophylaxis. In adjusted analyses, the effectiveness of i ntrapartum antibiotic prophylaxis was 86% (95% confidence interval, 66%-94% ). When the first dose of antibiotics was given greater than or equal to2 h ours before delivery, the effectiveness increased to 89% (95% confidence in terval, 70%-96%); when it was given within 2 hours of delivery, the effecti veness was 71% (95% confidence interval, -8%-92%). Effectiveness was lowest in mothers with intrapartum fever (72%, 95% confidence interval, -9%-93%). On the basis of a 70% prevalence of maternal risk factors expected among c ases in the absence of intrapartum antibiotic prophylaxis, we estimate that the risk-based strategy could reduce early-onset group B streptococcal dis ease by 60%. CONCLUSIONS: The risk-based approach to intrapartum antibiotic prophylaxis is effective in preventing early-onset group B streptococcal disease. To ac hieve the maximum preventive effect, the first dose of antibiotics should b e administered at least 2 hours before delivery.