During January and August, 1990, 23 cases of early onset Group B Strep
tococcus (GBS) disease occurred in a Kansas City, MO, hospital with an
attack rate of 14/1000 live births, compared with an annual rate of 1
.2 cases/1000 live births for 1988 through 1989. Case infants were com
pared with controls matched by birth weight, race, maternal age and da
y of delivery and to a second group of infants of mothers colonized wi
th GBS to identify risk factors and consider intervention strategies d
uring the outbreak. The presence of multiple serotypes among the invas
ive strains suggested that the outbreak was not caused by a common sou
rce. Case mothers were more likely than control mothers to have chorio
amnionitis, intrapartum fever or rupture of membranes >12 hours, and p
remature case infants were more likely to have a history of rupture of
membranes before onset of labor. Multiparous mothers of case infants
were more likely to have a history of spontaneous abortion (odds ratio
, 6.7; 95% confidence interval, 1.0 to 45.9). No single factor could e
xplain the increase in GBS disease. If intrapartum antibiotic prophyla
xis had been used for selected GBS carriers based on presence of eithe
r rupture of membranes >12 hours, intrapartum maternal fever or preter
m labor, 7.4% of all deliveries would have received antibiotics and 73
% of cases could potentially have been prevented. We conclude that ide
ntification of colonized mothers with perinatal risk factors and use o
f intrapartum antibiotics could be expected to prevent substantial dis
ease during an outbreak of early onset GBS disease.