Detection of group B Streptococcus during antenatal screening in Western Australia: a comparison of culture and molecular methods

J Appl Microbiol. 2019 Aug;127(2):598-604. doi: 10.1111/jam.14331. Epub 2019 Jun 14.


Aim: Global screening strategies for Group B Streptococcus (GBS) include risk- or culture-based methods to guide intrapartum prophylaxis. In Western Australia (WA), antenatal culture-based screening is routine; however, numerous culture methods exist, in addition to molecular methods. We aimed to assess the comparability of research and diagnostic screening approaches.

Methods and results: Vaginal and rectal swabs were self-collected by pregnant women (n = 531) from King Edward Memorial Hospital, WA, in parallel to routine screening (35-37 weeks of gestation). Research methods involved culture (Strep B Carrot Broth™ and StrepB CHROMagar™) and molecular methods (real-time PCR) and were compared to routine diagnostic screening (Lim Broth and Granada agar). Overall, GBS detection was comparable between research and diagnostic approaches (3-5% discrepancy, kappa = 0·76). Specificity/sensitivity of Carrot Broth was 100%/89%, while that of CHROMagar was 73%/100%, respectively. Direct PCR was unable to detect GBS in ~18% of specimens which were culture positive; however, it exhibited 100% specificity.

Conclusions: This clinical evaluation of GBS screening methods provides support for current practice.

Significance and impact of the study: Although CHROM was highly sensitive, further testing is recommended due to a high false-positive rate. Molecular assays are useful for rapid detection; however, low-titre samples may require additional enrichment prior to molecular analysis to improve sensitivity.

Keywords: Streptococcus agalactiae; GBS; antenatal; culture; group B Streptococcus; molecular; pregnant; screening.

Publication types

  • Comparative Study

MeSH terms

  • Female
  • Humans
  • Pregnancy
  • Pregnancy Complications, Infectious / diagnosis*
  • Prenatal Diagnosis*
  • Real-Time Polymerase Chain Reaction
  • Rectum / microbiology
  • Sensitivity and Specificity
  • Streptococcal Infections / diagnosis
  • Streptococcal Infections / diagnostic imaging*
  • Streptococcus agalactiae / genetics
  • Streptococcus agalactiae / isolation & purification*
  • Vagina / microbiology
  • Western Australia