Efficacy of intrapartum chemoprophylaxis less than 4 hours duration.

Objective. Current guidelines for prevention of group B streptococcus (GBS) early-onset infection recommend to administer antibiotic during labor at least 4 h prior to delivery (adequate prophylaxis). We aimed to determine if neonatal GBS colonization may be significantly decreased in case of inadequate (<4 h) duration of ampicillin prophylaxis.Methods. In prospective, cohort study, 167 infants born to 167 GBS culture-positive mothers without additional risk factors were enrolled. Cultures were collected both, at 10–24 h after birth (admission) and at discharge.Results. Among 137 infants born to mothers who received inadequate prophylaxis, 5 (3.6%, C.I. = 0.5–6.8) were colonized (≥1 sites) at admission, at discharge, or both, at admission and discharge. Eighty-two women received prophylaxis <2 h before delivery and two infants (2.4%) were colonized at discharge.Eighteen (60.0%, C.I. = 42.5–77.5) of 30 infants who were not exposed to prophylaxis were colonized at admission or both, at admission and discharge.Colonization was significantly more frequent among infants born to untreated mothers with respect to infants born to women who received inadequate prophylaxis (either <2 or <4 h).Conclusions. In this selected group, inadequate prophylaxis significantly interrupted vertical colonization. This effect was evident even if prophylaxis started <2 h before delivery.