Epidemiology of group B Streptococcus: longitudinal observations during pregnancy.

A longitudinal, three-year study of the epidemiology of group B Streptococcus was conducted with repeated (four to 11) observations of 382 patients followed through pregnancy, delivery, and the postpartum period. Group B streptococci (2.3% of which were nonhemolytic) were isolated from the birth canal at first visit from 15% of the patients and from 28% with repeated cultures. Overall, group B streptococci were isolated at 12% of culture visits. Streptococcal carriage was significantly less common among patients who were Mexican-American, 20 years old or older, or in a fourth or later pregnancy. Multivariate analysis indicated that each of these three factors had a significant, independent bearing upon carriage of group B streptococci. Of 108 patients harboring these organisms in the birth canal, 36% could be classified as chronic, 20% as transient, and 15% as intermittent carriers. The relationship of infant colonization to the presence of streptococci in the birth canal at delivery and not to previous or subsequent carriage by the mother was consistent with the observation that maternal colonization was often inconstant.