Abstract 973 Poster Session II, Sunday, 5/2 (poster 97)

Early onset disease (EOD) caused by Group B streptococcus (GBS) occurs only in infants who are surface colonized at birth. The attack rates of EOD is 8-12 times higher among heavily colonized (>=3 of 4 sites being positive)than in lightly colonized newborns (<=2 of 4 sites). We conducted a case-control study to investigate the determinants of EOD among infants exposed to high inocula of GBS by comparing infants who were heavily surface colonized at birth without EOD (control) with infants with EOD (case). Cases were identified by active surveillance of microbiology laboratories and intensive care nurseries in 14 hospitals within 6 academic centers between 7/19/95 and 12/31/97. Colonized infants were identified by systematic culturing of a sample of infants each month. Cultures were taken from throat, anus, umbilicus and ear before the first bath. Maternal and infant characteristics were extracted from the medical records. During the study period, 106 infants with EOD were identified among 97,919 births; 826 lightly (<= 2 of 4 sites) colonized and 499 heavily (>=3 of 4 sites) colonized infants without EOD were identified among 13,138 surface cultured infants. In univariate analyses, case-infants were born significantly more often (P < 0.05) to mothers who were primigravidas, nulliparous, on Medicaid or public assistance, membranes ruptured >= 12 hrs, had intrapartum fever or maternal infection, fetal distress, or received intrapartum antibiotics. Case-infants were also significantly more likely to be <2500 grams, <34 weeks gestation, or born by C-section. 99% of both case-mothers and control-mothers had prenatal care. Case-mothers tended to be younger (<20 years of age, 24% vs 15%, P=0.1), or to require insulin during pregnancy (4.7% vs 2.4%, P =0.2). In multivariate logistic regression analyses, the following variables were independently associated with risk of EOD: intrapartum infection, C-section, gestational age <34 weeks, and rupture of membranes (ROM)>=12 hours (Table). These data indicate that several factors (intrapartum infection, gestational age <34 weeks, C-section, ROM >=12 hours)increase the likelihood of disease once exposure occurs. Although future analysis of this data may be impacted by maternal GBS type-specific antibody level, risk factors such as C-section, ROM >=12 hrs instead of 18 hrs that are not in the current recommendations for intrapartum antibiotic prophylaxis should be considered in the future for the prevention of early-onset GBS disease.

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