For two decades streptococci classified serologically as Lancefield group B Streptococcus agalactiae (GBS) have been a leading cause of perinatal infections. In neonates and young infants these infections include congenital pneumonia, sepsis, or meningitis; in pregnant women they include urinary tract infection, chorioamnionitis, early postpartum endometritis, postcesarean section febrile morbidity, and—less frequently—pelvic thrombophlebitis or endocarditis. Although the incidence varies somewhat by geographic region, 12 000 infants and 50 000 pregnant women in the United States are estimated to develop GBS-associated morbidity or mortality annually.1 Overall mortality for early-onset (less than 7 days of age) and late-onset (7 days to 3 months of age) infant disease is approximately 15% and 10%, respectively.2-4 Gestational age significantly correlates with mortality among early-onset cases and is approximately 25% to 30% in preterm infants and 2% to 8% in term infants. Thus, every year approximately 1 600 infants die and an equal number have permanent neurologic sequelae following meningitis.1 This substantial GBS-associated perinatal mortality and morbidity make prevention strategies imperative. Among proposed strategies, including chemoprophylaxis and immunoprophylaxis, only intrapartum maternal chemoprophylaxis has been evaluated for safety and efficacy.
GBS are frequently harbored in the genitourinary and lower gastrointestinal tracts of adults. When sensitive culture methods are used for their detection (ie, antibiotic-containing or selective broth media) and both lower vaginal and anorectal sites are sampled, GBS are found in 15% to 40% of pregnant women.5-8 Direct plating of swabs from body surfaces onto solid media or sampling of the cervix as a single genital tract site fails to identify as many as 50% of women who are culture-positive for GBS.4