Background Child survival rates have improved globally, but neonatal mortality due to infections, such as group B Streptococcus (GBS), remains a significant concern. The global burden of GBS-related morbidity and mortality is substantial. However, data from low and middle-income countries is lacking. Vaccination during pregnancy could be a feasible strategy to address GBS-related disease burden. Methods We assessed maternal rectovaginal GBS colonization and neonatal disease rates in a prospective cohort of 6062 women-infant pairs. Surveillance for invasive infant disease occurred in parallel at two Kampala hospital sites. In a nested case-control study, we identified infants <90 days of age with invasive GBS disease (iGBS) (n=24) and healthy infants born to mothers colonized with GBS (n=72). We measured serotype-specific anti-capsular immunoglobulin G in cord blood/infant sera using a validated multiplex Luminex assay. Results We found a high incidence of iGBS (1.0 per 1,000 live births) within the first 90 days of life across the surveillance sites, associated with a high case fatality rate (18.2%). Maternal GBS colonization prevalence was consistent with other studies in the region (14.7%; 95% confidence interval 13.7-15.6%). IgG geometric mean concentrations were lower in cases than controls for serotypes Ia (0.005 vs 0.12 µg/mL; p=0.05), III (0.011 vs 0.036 µg/mL; p=0.07) and in an aggregate analysis of all serotypes, (0.014 vs 0.05 µg/mL; p=0.02). Conclusions We found that GBS is an important cause of neonatal and young infant disease in Uganda and confirmed that maternally derived antibodies were lower in early-onset GBS cases than in healthy exposed controls
