Maternal Antibody at Delivery Protects Neonates From Early Onset Group B Streptococcal Disease

Background. Further reduction in the group B streptococcal (GBS) disease burden in neonates in the United States awaits an additional prevention strategy, such as maternal immunization. Methods. We performed a prospective, multicenter, case-control study of 33 mothers delivering neonates with early onset GBS infection (cases), and 99 age- and ethnicity-matched mothers colonized with the same capsular polysaccharide (CPS) types delivering healthy neonates (controls). Relative risk and absolute risk were calculated for early onset disease associated with concentrations of type Ia, III, or V CPS-specific antibody in maternal serum. Results. For GBS types Ia and III, maternal CPS-specific antibody concentrations of >= 0.5 mu g/mL were associated with a relative risk of approximately 0.1 (95% confidence intervals [CIs], .01-.74 and 0-.72, respectively; P = .02 for each), corresponding to a 90% risk reduction (by logistic regression). For type V, the relative risk was 0.3 (95% CI, .01-3.1), corresponding to a 70% risk reduction. By Bayesian modeling, the risk of early onset disease would decrease by 70% if maternal CPS-specific antibody concentrations for these 3 GBS types were >= 1 mu g/mL. Conclusions. Maternal CPS-specific antibody serum concentrations of >= 1 mu g/mL at the time of delivery appear to protect most neonates from early onset GBS type Ia and III disease.