Preventing early-onset group B streptococcal sepsis: strategy development using decision analysis

Abstract

Objective: To evaluate recommended strategies for prevention of early-onset group B streptococcal infections (EOGBS) with reference to strategies optimized using decision analysis.

Methods: The EOGBS attack rate, prevalence and odds ratios for risk factors, and expected effects of prophylaxis were estimated from published data. Population subgroups were defined by gestational age, presence or absence of intrapartum fever or prolonged rupture of membranes, and presence or absence of maternal group B streptococcus (GBS) colonization. The EOGBS prevalence in each subgroup was estimated using decision analysis. The number of EOGBS cases prevented by an intervention was estimated as the product of the expected reduction in attack rate and the number of expected cases in each group selected for treatment. For each strategy, the number of residual EOGBS cases, cost, and numbers of treated patients were calculated based on the composition of the prophylaxis group. Integrated obstetrical-neonatal strategies for EOGBS prevention were developed by targeting the subgroups expected to benefit most from intervention.

Results: Reductions in EOGBS rates predicted by this decision analysis were smaller than those previously estimated for the strategies proposed by the American Academy of Pediatrics in 1992 (32.9% vs 90.7%), the American College of Obstetricians and Gynecologists in 1992 (53.8% vs 88.8%), and the Centers for Disease Control and Prevention in 1996 (75.1% vs 86.0%). Strategies based on screening for GBS colonization with rectovaginal cultures at 36 weeks or on use of a rapid test to screen for GBS colonization on presentation for delivery, combining intrapartum prophylaxis for selected mothers and postpartum prophylaxis for some of their infants, would require treatment of fewer patients and prevent more cases (78.4% or 80.1%, respectively) at lower cost.

Conclusions: No strategy can prevent all EOGBS cases, but the attack rate can be reduced at a cost <$12 000 per prevented case. Supplementing intrapartum prophylaxis with postpartum ampicillin in a few infants is more effective and less costly than providing intrapartum prophylaxis for more mothers. Better intrapartum screening tests offer the greatest promise for increasing efficacy. Integrated obstetrical and neonatal regimens appropriate to the population served should be adopted by each obstetrical service. Surveillance of costs, complications, and benefits will be essential to guide continued iterative improvement of these strategies.