Streptococcus agalactiae (also known as group B streptococcus or GBS) is a Gram-positive, ß-hemolytic bacteria that is typically found in the human intestinal and genitourinary tract as a part of commensal microbiota. However, it can cause severe opportunistic infections in immunocompromised, elderly, and neonatal populations. In fact, GBS is the leading cause of neonatal infections, known as the early-onset GBS (EOGBS). It has been estimated that rates of EOGBS vary from 0.23 to 3.0 per 1,000 live births.

National guidelines recommend the universal antenatal screening for GBS between 35 and 37 week’s gestation, which has traditionally been conducted with a standard culture method. However, this method is time-consuming and thus prone to “false-negative results” as it does not reflect the colonisation status at the time of delivery. Hence, intrapartum molecular PCR tests are increasingly being used, as they provide rapid test results which accurately reflect the intrapartum GBS colonisation status at the time of delivery. The GenomEra GBS Assay Kit, performed on the GenomEra CDX System, is a qualitative in vitro diagnostic (IVD) nucleic acid test for the detection of GBS from:

  • Vaginal-rectal swab samples collected into Copan ESwab transport medium from pregnant intrapartum or antepartum women
  • Enrichment broth cultures from vaginalrectal swab samples collected from antepartum women.

The test uses automated homogeneous PCR to detect a specific region of the S. agalactiae genome, ensuring coverage of the GBS strains. All reagents required for performing the amplification and detection steps are contained in dry form in the GenomEra GBS Test Chips, including an Internal Amplification Control of a nonnaturally existing DNA sequence to monitor for assay inhibition. The assay sequence takes around 50 minutes and ends with automatic, qualitative reporting of results.

Recently, studies by Andreasen (2019), Nielsen (2020), Hartvigsen (2022), and Koliwer-Brandl (2023) have reported observations from using the kit for detection of GBS in pregnant women during delivery. In these studies, a total of 663 intrapartum vaginal or rectovaginal swabs were collected from pregnant women at the time of delivery and analysed without any broth preenrichment steps with a standard culture, GenomEra GBS Assay Kit, and either BD MAX GBS or GeneXpert GBS assays.

Taken together, these studies demonstrated the effectiveness of molecular assays for the rapid detection of GBS in pregnant women during delivery. The overall sensitivity and specificity of the GenomEra GBS Assay Kit was 86.1% and 98.9%, respectively, as compared with the culture. In comparison with the other two PCR assays, no significant differences in the sensitivity or specificity of the methods were observed. Interestingly, the invalid rate was significantly lower with the GenomEra assay than with the other PCR assays. This may be explained by the unique sample preparation protocol utilised in the GenomEra GBS Assay Kit which makes the assay less susceptible to PCR inhibition caused by mucus in a specimen. Particularly, the low number of erroneous results is an important aspect when assessing the feasibility of rapid GBS testing. The therapeutic implication of an invalid test result may require initiation of intrapartum antibiotic prophylaxis since typically there is no time to wait for a repeated test result in a clinical setting with women in delivery.

According to the studies, the GenomEra system is easy to use and suitable for a maternity ward after training of midwives. With a straightforward testing set-up, PCR screening for GBS can be conducted to all women in delivery immediately upon admittance to the ward, particularly in highrisk countries or areas where antibiotics are available but the intensive care unit for infants with EOGBS is not accessible.

Using molecular assays like the GenomEra GBS Assay Kit can help to reduce the risk of neonatal infection, allowing for prompt treatment and improved outcomes.