Epidemiology of early-onset neonatal group B streptococcal infection: implications for screening.

OBJECTIVE: To determine the difference in outcomes between universal screening and risk-based assessment for prenatal group B streptococcus (GBS) infection based on the epidemiology of early-onset GBS infection in Winnipeg, Man, and to examine its implications for prenatal GBS screening.
DESIGN: Retrospective random chart audit of 330 women receiving intrapartum hospital care and retrospective chart audit of all infants with early-onset neonatal GBS disease over 2 years.
SETTING: Each of the 3 hospitals in Winnipeg, Man, offering intrapartum services. MAIN OUTCOME MEASURES: Maternal charts were audited for history of prenatal GBS screening, GBS status, clinical risk factors for neonatal GBS transmission, and use of intrapartum antibiotics to prevent neonatal GBS infection. Neonatal GBS records were audited for maternal clinical risk factors for GBS transmission, history of maternal GBS screening and GBS status, use of maternal intrapartum antibiotic prophylaxis, and neonatal outcome.
RESULTS: Screening revealed a 26% GBS carrier rate in our population. Among these carriers, 70% (or 18% of the population) had no other clinical risk factors for neonatal GBS transmission. The transmission rate for untreated GBS-positive women was 1.74 per 1000 women. The differences in outcomes between universal and risk-based screening were small in our population. A total of 3449 women would require universal screening to prevent a single case of early-onset neonatal GBS disease that would occur if a risk-based approach were used (3 cases per year). This number increases to 68,966 to prevent a single GBS-related death (1 case in 7 years). An additional 679 women would receive intrapartum prophylactic antibiotics per year with universal screening than would have received antibiotics with a risk-based approach.
CONCLUSION: The differences in neonatal GBS transmission rates resulting from universal versus risk-based screening in Winnipeg require universal screening of many women for results to become apparent. Universal screening and antibiotic prophylaxis of all GBS carriers result in increased antibiotic exposure in our population, which might carry its own risks. Therefore, patients should be involved in decisions on whether to be screened based on identification of risks and benefits.