Objective: To compare the Center for Disease Control consensus guidelines' screening-based strategy to a risk-based strategy as regards the incidence of early-onset group B streptococcus (GBS) infection among term infants.
Study design: A cohort of university hospital prenatal clinic mother-infant pairs who were screened for GBS at 35 to 37 weeks' gestation were compared to a matched control group of unscreened mother-infant pairs from the outreach satellite prenatal clinics who delivered at the same institution during the same time period. GBS screening was carried out with rectovaginal cultures plated on selective media. GBS-positive women received antimicrobial prophylaxis in labor whereas women of unknown GBS status were only treated intrapartum if they had a risk factor for GBS infection. Principal outcome variables included incidence of cases of neonatal early-onset GBS sepsis (blood, urine, or cerebrospinal fluid positive for GBS), incidence of cases of strongly suspected GBS sepsis (culture negative), and incidence of neonatal sepsis with non-GBS organisms.
Results: There were 3164 screened mother-infant pairs who were compared to 2684 unscreened pairs. The incidence of GBS carriage was 13.3%. A random sample of 420 screened women were compared to a matched sample of 407 women of unknown GBS carrier status for characterization of demographics and risk factors. No cases of documented GBS sepsis occurred in the infants of the screened women, but four cases occurred among the infants of the women who did not undergo screening (incidence 1.5/1000) (p = 0.04), only one of whom had a risk factor for GBS infection. Cases of suspected but culture negative sepsis were not more common in the screened population when compared to the unscreened. There was one case of Escherichia coli sepsis in an infant of a mother in the unscreened group.
Conclusions: GBS screening at 35 to 37 weeks, with intrapartum antimicrobial prophylaxis of carriers, decreased the incidence of neonatal early-onset GBS sepsis and appears to have advantages over treatment based on risk factors alone in term infants.