Changing epidemiology of group B streptococcal colonization

Objectives. To define factors influencing vertical transmission of and neon atal colonization with group B streptococci (GBS) in neonates representing ethnically and economically diverse populations, and to determine the serot ype distribution of isolates, especially new types IV-VIII. Study Design. Prospective, cross-sectional study of neonates born to women evaluated for GBS colonization at admission for delivery to one of four hos pitals between January 1994 and February 1995. Cultures of throat, umbilicu s, and rectum were obtained from 24- to 48-hour-old infants for isolation o f GBS. Isolates were classified by capsular polysaccharide (I-VIII) and C p rotein (alpha and beta) antigen components. Results. Colonization was detected in 28% of 546 mothers, was higher in bla cks than whites (40.6% vs 20.3%) and Hispanics (26.9%), and was not influen ced by socioeconomic status. Overall, ethnic origin did not seem to be rela ted to GBS serotype, but whites were more likely to carry the new type V st rain than blacks (6 out of 24 [25%] vs 1 out of 43 [2%]). Vertical transmis sion of GBS to neonates was significantly diminished when their mothers had intrapartum antibiotics (0% vs 52%), rupture of membranes <12 hours before delivery (38.4% vs 73.3%), or delivery by cesarean section (25.9% vs 45.2% ). Colonization with GBS was found in 13.8% of 549 neonates, was acquired v ertically in 97%, and was less frequent in neonates at the private hospital s (4% vs 20%) where intrapartum antibiotics were given more frequently (34. 7% vs 17.3%). Among isolates from neonates, serotype Ia predominated (31.6% ) followed by types II (25%), III (22.4%), and V (11.8%); similar to 40% of strains contained C protein antigen, Conclusions. Changes in the epidemiology of GBS colonization included dimin ished rates in some populations associated with use of maternal intrapartum antibiotics, and a shift in serotype prevalence, with Ia as predominant an d V, in addition to II and III, as common.