Association of intrapartum antibiotic exposure and late-onset serious bacterial infections in infants.

Objective: Recommendations to prevent vertical transmission of group B Streptococcus (GBS) infections have resulted in many women's receiving antibiotics during labor with an associated reduction in early-onset GBS infections in their newborn infants. However, a potential relationship of intrapartum antibiotics (IPA) to the occurrence of late-onset (7-90 days) serious bacterial infections (SBIs) in term infants has not been reported. The objectives of this study were to determine whether infants with late-onset SBI were more likely than healthy control infants to have been exposed to IPA and whether there was a greater likelihood of antibiotic resistance in bacteria that were isolated from infants who had an SBI and had been exposed to IPA compared with those who had not.

Methods: We used a case-control design to study the first objective. Cases were previously healthy full-term infants who were hospitalized for late-onset SBI between the ages of 7 and 90 days. Control subjects were healthy full-term infants who were known not to have an SBI in their first 90 days. Cases and control subjects were matched for hospital of delivery. In the second part of the study, rates of antibiotic resistance of bacteria that were isolated from infected infants were compared for those who had and had not been exposed to IPA.

Results: Ninety case infants and 92 control subjects were studied. Considering all types of IPA, more case (41%) than control infants (27%) had been exposed to IPA (adjusted odds ratio [OR]: 1.96; 95% confidence interval [CI]: 1.05-3.66), after controlling for hospital of delivery. The association was stronger when IPA was with broad-spectrum antibiotics (adjusted OR: 4.95; 95% CI: 2.04-11.98), after controlling for hospital of delivery, penicillin IPA, maternal chorioamnionitis, and breastfeeding. Bacteria that were isolated from infected infants who had been exposed to IPA were more likely to exhibit ampicillin resistance (adjusted OR: 5.7; 95% CI: 2.3-14.3), after controlling for hospital of delivery, but not to other antibiotics that are commonly used to treat SBI in infants.

Conclusions: After adjusting for potential confounders, infants with late-onset SBI were more likely to have been exposed to IPA than noninfected control infants. Pathogens that cause late-onset SBI were more likely to be resistant to ampicillin when the infant had been exposed to intrapartum antibiotics.