Antibodies to capsular polysaccharides of group B Streptococcus in pregnant Canadian women: Relationship to colonization status and infection in the neonate

In a cohort study of 1207 pregnant women in Alberta, Canada, the serotype d istributions of vaginal-rectal group B Streptococcus (GBS) isolates were co mpared with all isolates from neonates with invasive GBS disease identified by population-based surveillance. Serum concentrations of Ia, Ib, II, III, and V capsular polysaccharide (CPS)-specific IgG also were determined, acc ording to serotype of the vaginal-rectal colonizing GBS strain. GBS coloniz ation was detected in 19.5% (235 of 1207) of women. Serotype III accounted for 20.6% (48 of 233) of colonizing strains available for typing but for 37 % (27 of 73) of invasive isolates from neonates (P < .01). Maternal coloniz ation with type III was least likely to be associated with moderate concent rations of III CPS-specific IgG. Serotype III GBS is more invasive than oth er serotypes in this population; this may be due, at least in part, to poor maternal type III CPS-specific antibody response.