The Association Between Breast Milk Group B Streptococcal Capsular Antibody Levels and Late-onset Disease in Young Infants

Background Animal-model studies have demonstrated less group B streptococcal (GBS) invasive disease and gastrointestinal colonization after enteral administration of serotype-specific capsular antibodies. There is, however, a paucity of information on the association of breast milk GBS serotype-specific capsular antibodies and risks for invasive disease in infants. The aim of this study was to explore the association between natural secretory immunoglobulin A (sIgA) capsular antibodies in breast milk and the occurrence of late-onset disease (LOD) in young infants. Methods A matched case-control study was undertaken in infants Results Breast milk samples were available for 31 LOD cases (8 serotype Ia and 23 serotype III), 21 recto-vaginally colonized matched controls (10 serotype Ia and 11 serotype III), and 84 serotype Ia and 105 serotype III noncolonized matched controls. Using a Bayesian model to estimate the probability of disease, there were 90% reductions in the risks of developing serotypes Ia and III LOD with sIgA concentrations ≥0.14 µg/mL and ≥2.52 µg/mL, respectively. Conclusions Breast milk sIgA capsular antibodies were associated with lower risks for LOD in young infants. The ability of GBS polysaccharide-protein conjugate vaccines currently under development to induce sIgA responses warrant investigation as potential mediators of protection against LOD.