Group B Streptococcus detection in pregnant women via culture and PCR methods

Group B Streptococcus (GBS), a source of neonatal infection, colonizes the gastrointestinal and genitourinary tracts of pregnant women. Routine screening for maternal GBS in late pregnancy and consequent intrapartum antibiotic prophylaxis have reduced the incidence of early-onset GBS neonatal infection. The aim of this study was to evaluate the performance of PCR, compared to culture (gold standard), in GBS colonization screening of pregnant women, and to establish the prevalence of GBS colonization among this population.

Vaginal introitus and perianal samples were collected from 204 pregnant women, between the 35th and 37th weeks of pregnancy, at the Obstetrics and Gynecology Unit of the University of Caxias do Sul General Hospital between June 2008 and September 2009. All samples were cultured after enrichment in a selective medium and then assayed by culture and PCR methods.

The culture and PCR methods yielded detection rates of vaginal/perianal GBS colonization of 22.5% and 26%, respectively (sensitivity 100%; specificity 95.6%; positive and negative predictive values 86.8% and 100%, respectively). A higher prevalence of GBS colonization was detected in the combined vaginal and perianal samples by both culture and PCR assay analyses.

PCR is a faster and more efficient method for GBS screening, allowing for optimal identification of women who should receive intrapartum antibiotic prophylaxis to prevent newborn infection.