Changing epidemiology of group B streptococcal colonization

To define factors influencing vertical transmission of and neonatal colonization with group B streptococci (GBS) in neonates representing ethnically and economically diverse populations, and to determine the serotype distribution of isolates, especially new types IV-VIII.

Prospective, cross-sectional study of neonates born to women evaluated for GBS colonization at admission for delivery to one of four hospitals between January 1994 and February 1995. Cultures of throat, umbilicus, and rectum were obtained from 24- to 48-hour-old infants for isolation of GBS. Isolates were classified by capsular polysaccharide (I-VIII) and C protein (alpha and beta) antigen components.

Colonization was detected in 28% of 546 mothers, was higher in blacks than whites (40.6% vs 20.3%) and Hispanics (26. 9%), and was not influenced by socioeconomic status. Overall, ethnic origin did not seem to be related to GBS serotype, but whites were more likely to carry the new type V strain than blacks (6 out of 24 [25%] vs 1 out of 43 [2%]). Vertical transmission 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 vertically in 97%, and was less frequent in neonates at the private hospitals (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%); approximately 40% of strains contained C protein antigen.

Changes in the epidemiology of GBS colonization included diminished rates in some populations associated with use of maternal intrapartum antibiotics, and a shift in serotype prevalence, with Ia as predominant and V, in addition to II and III, as common.