Maternal and Newborn Group B Streptococcus Serology in the United States and South Africa

Background This descriptive seroepidemiology study characterized group B Streptococcus (GBS) capsular antibody levels in pregnant individuals and their newborns. Methods Healthy US and South African ≥18-year-olds at ≥34 weeks of pregnancy were enrolled. Exploratory analyses evaluated GBS serotype-specific (Ia, Ib, II, III, IV, V) anti-capsular polysaccharide (CPS) immunoglobulin G (IgG) geometric mean concentrations (GMCs) before and at delivery and in cord blood; newborn-to-maternal transplacental transfer ratios were determined. Results We enrolled 722 maternal (US, n=273; South Africa, n=449) and 592 newborn participants (n=251; n=341). Maternal GBS anti-CPS IgG GMCs were similar before and at delivery. A trend for higher GMCs (serotypes Ia, Ib, II, III) among South African compared with US maternal participants was seen. As in maternal participants, GMCs for serotypes Ia and III trended higher among South African compared to US newborns. Mean transplacental transfer ratios were higher for US newborn−maternal pairs compared with South African dyads. Transplacental transfer ratios for serotypes Ia and Ib were >1 for US pairs. Among US participants, there was a trend for higher transplacental transfer ratios among White versus Black participants. Maternal hypergammaglobulinemia (gamma globulin >1.35 g/dL) was observed in 23.8% of South African participants and in no US participants. Conclusions GBS serotype-specific IgG GMCs varied by region and serotype; reasons for observed regional differences are likely multifactorial, including variations in baseline antibodies and transplacental transfer efficiency. Understanding these variations may inform efforts for maternal immunization strategies aimed at enhancing neonatal antibody concentrations.