Group B streptococcal colonization and serotype-specific immunity in pregnant women at delivery

Objective: To describe the relationship between serum concentration of grou p B streptococcal capsular polysaccharide-specific immunoglobulin (Ig) G, c olonization status, race or ethnicity, and age in pregnant women. Methods: Pregnant women (n = 3307) were enrolled from geographically and et hnically diverse populations. At the time of admission for delivery, swabs of the lower vagina and rectum were obtained for isolation of group B strep tococci. In a subset of women whose sera were available, capsular polysacch aride-specific IgG concentrations were quantified by serotype-specific (Ia, Ib, II, III, and V) enzyme-linked immunosorbent assay and compared by grou p B streptococcal colonization status. Results: Group B streptococcal colonization was detected in 856 women (26%) , and the rate was significantly higher among black women (37%) than in oth er racial or ethnic groups (odds ratio 1.7, 95% confidence interval 1.4, 2. 1). Colonization status did not differ by study site or age. Colonization w ith serotypes Ia, II, III, or V was associated with significantly higher se rum concentrations of IgG specific for the capsular polysaccharide of the c olonizing serotype compared with noncolonization. However, 48% of colonized women had low capsular polysaccharide-specific IgG levels (less than 0.5 m u g/mL) in their delivery sera. Colonized teenagers had the lowest median c oncentration. Conclusion: Colonization with group B streptococcus can elicit a systemic i mmune response, with a cumulative increase in the prevalence of capsular po lysaccharide-specific IgG with increasing age. Conversely, low antibody lev els in colonized teenagers might account in part for the reported increased risk of group B streptococcal disease in neonates born to these patients. (Obstet Gynecol 2000;96:498-503. (C) 2000 by The American College of Obstet ricians and Gynecologists.).