Antenatal group B streptococcus detection in pregnant women: culture or PCR?

Abstract

Introduction: Group B streptococcus (GBS) is an important cause of neonatal infections. Maternal GBS colonization screening and intrapartum antimicrobial prophylaxis of colonized women can prevent neonatal diseases. The aim of this study was to assess the prevalence of GBS colonization in pregnant and non-pregnant women and to compare the performance of a polymerase chain reaction (PCR) assay with the established as gold standard technique, culture method, used for the detection of this microorganism.

Methodology: Vaginal and rectal samples collected from 857 pregnant and 370 non-pregnant women were examined through cultures, while the samples collected from 452 pregnant women between 35 and 37 weeks of gestation were assayed by culture and PCR method targeting the cfb gene.

Results: GBS colonization was present in both pregnant and non-pregnant women. The colonization rate was similar in non-pregnant and first trimester pregnant women and then increased from first to the third trimester of pregnancy. GBS cultures for vaginal and rectal samples were positive in 13.2% and 14.3% in non-pregnant women, while in pregnant women 13.2% and 13.7% in the first trimester, and 15.0% and 16.5% in the second trimester, respectively. In third trimester pregnant women, compared to culture method, PCR identified a significantly increased number of GBS positive vaginal (18.4% vs 22.6%, p = 0.0006) and rectal (18.1% vs 21.2%, p = 0.01) samples.

Conclusions: GBS colonization rate was higher in the third trimester. PCR proved to be a rapid and useful GBS screening method allowing a shorter detection time, while identifying more colonized women than culture.

Keywords: Group B streptococcus; Polymerase Chain Reaction; cfb gene; neonatal disease; pregnancy; vaginal culture.