Group B streptococcal carriage and disease: a 6-year prospective study.

A prospective study of group B streptococcal (GBS) carriage and disease was conducted over 6 years. Carriage rates at delivery for mothers and infants were 20% and 12%, respectively. Forty-five cases of GBS disease occurred in infants, 24 "early-onset" disease and 21 "late-onset" disease. The combined attack rate for early and late disease was 3.3 per 1000 live births over the 6 years. The rate of early-onset disease was highest in infants found to be heavily colonized at birth: 50 per 1000 live births. Twenty-three of 24 had evidence of intrauterine-acquired infection. All GBS serotypes were represented. Preterm delivery, prolonged labor, premature rupture of membranes, and maternal infection enhanced the risk of early disease. Septicemia was the predominant form of late-onset disease (15 of 21 cases); GBS type III accounted for 19 of 21 cases. Ten of 21 infants with late infections were colonized at birth with the GBS type that subsequently caused disease. Thus a maternal source of infection was identified in 34 of the 45 infants. These data reveal consistent year-to-year carriage and disease rates in the study population.