Factors associated with intrapartum transmission of group B Streptococcus

Data regarding the minimum duration of intrapartum antibiotic prophylaxis (IAP) required for preventing group B Streptococcus (GBS) early-onset sepsis are conflicting. Understanding factors that influence neonatal colonization (NC) might help us understand factors associated with failure of prophylaxis.

This is a 14-month prospective cohort study conducted at a single tertiary care center with a screening-based strategy. Women were enrolled if they had ≥ 35 weeks' gestation and were GBS-positive at the vaginal site on admission. Their neonates were cultured from the throat and rectum at 24-48 h after birth. Colony growth was graded semiquantitatively (from 1+ to 4+). Uni- and multivariate logistic regression analyses were performed to evaluate risk factors for NC.

There were 502 neonates, 458 of whom were exposed to IAP. All cases of NC were associated with a lack of IAP exposure (P < 0.01), intrapartum fever ≥ 37.5°C (P < 0.01) and African ethnicity (P < 0.01). In the 458 IAP-exposed neonates, the rates of NC were low and did not vary significantly in the range of less than 1-12 h before delivery (score test for trend of odds, P = 0.13). The only independent factors associated with NC were intrapartum fever ≥ 37.5°C and heavy maternal colonization (P < 0.01 and P = 0.03, respectively).

Heavy maternal colonization, intrapartum fever, African ethnicity and lack of IAP exposure were associated with GBS transmission in neonates born to women who were tested positive on admission. Low rates of NC were found among IAP-exposed neonates irrespective of IAP duration.