Immunological investigation of infants with septicemia or meningitis due to group B Streptococcus.

Purified polysaccharide from type III group B Streptococcus contains both a type III-specific determinant and another determinant that is common to strains of serotypes other than type III. The polysaccharide contains sialic acid, galactose, heptose, glucose, glucosamine, and mannose. Serum antibody to this antigen was measured by means of a radioactive antigen-binding assay. Sera from 36 (67.9%) of 53 women with healthy newoborns contained antibody, a prevalence significantly different from that in sera from 15 women (13.3%) whose neonates developed septicemia or meningitis due to type III group B Streptococcus. Complete concordance for presence or absence of anticapsular antibody in sera from 14 women at delivery and in their neonates' cord sera was demonstrated; this concordance indicates transplacental transfer of antibody. Sera from each of four adults with invasive infection who were studied during convalescence contained antibody to the capsular polysaccharide of type III group B Streptococcus. In contrast, antibody was absent from 10 infants who had recovered from bacteremia, septicemia, and/or meningitis due to type III group B Streptococcus.