How will you support more accurate GBS screening?

NAAT testing is a powerful tool in reducing GBS false negative results

The adoption of new clinical practice relies on clinical evidence and knowledgeable champions. Despite documented increases in test sensitivity, the potential to reduce adverse clinical outcomes and greater laboratory efficiency, approximately 81% of labs do not use a nucleic acid amplified test (NAAT) for GBS screening.1,2 Fortunately, lab leaders are emerging as champions of this screening tool for mothers and infants.

Group B Streptococcus (GBS) is a Gram-positive bacterium that colonizes the lower genital tract of approximately 25% of women in the US.3 If left untreated, GBS can cause maternal and fetal infection, and early-onset neonatal disease (EOD), which can endanger the lives of newborns.4 Mortality from EOD has fallen steeply in the past 50 years, thanks to US screening protocols.5 Screening tests have evolved beyond culture testing to incorporate molecular NAATs for even greater clinical and operational benefits.

The limitations of traditional culture-based testing

There is considerable consensus among US professional societies including the American Society for Microbiology (ASM), ACOG (American College of Obstetricians and Gynecologists), and the Center for Disease Control (CDC) that GBS screening is recommended between 36 0/7 and 37 6/7 weeks of gestation.5,6,7 While traditional testing by culture alone is frequently used to meet these screening recommendations, data support the use of highly sensitive NAATs for GBS screening.

When GBS is detected, intravenous antibiotics administered to the mother during labor can prevent most cases of GBS EOD in newborns.7 However, ASM guidelines suggest that the sensitivity of culture tests may be as low as 53-70%.6 Labs can look towards a more sensitive screening protocol by implementing NAAT methods.

Using NAAT to increase test accuracy

NAAT technology is a powerful ally in reducing false negative results to ensure that GBS-positive mothers receive critical prophylaxis, while GBS-negative mothers avoid unnecessary antibiotics. In a 2019 study of PCR NAATs for GBS detection, authors from The University of California San Diego concluded that the method is highly sensitive and should be considered the preferred method for prenatal GBS screening.8

Intravenous penicillin is the current antibiotic of choice for intrapartum prophylaxis in GBS-positive women.6 Fewer than 1% of the population is estimated to be truly allergic to penicillin, but for this small cohort of pregnant women, it is necessary to perform GBS antimicrobial susceptibility testing (AST) to guide appropriate alternate antibiotic therapy.6,9  Since AST requires isolation of viable organisms and growth in culture, laboratories could consider implementing a modified algorithm to include parallel NAAT and culture with AST in these rare cases.

GBS screening

Laboratory workflow benefits of NAAT for GBS screening

For labs impacted by staffing shortages, NAAT is one way to do more with less. Automated NAATs eliminate hands-on culture plate preparation time, increase throughput, and speed up the time to result.8 After the 18 to 24-hour culture enrichment step, the lab can report results in as little as 3-hours. Automation reduces operator subjectivity and re-tests while minimizing transcription errors when the results, which require no interpretation, can be printed or downloaded.10


Laboratory professionals may want to guide the discussion with their physicians about the optimal use of the available test methods, depending on the mother’s medical history. For example, laboratorians are able to help to define electronic health record-embedded workflows such as making the indication of penicillin allergy a mandatory field in electronic orders, as per the recommendations in ASM guidelines.6 Take the example of a standardized allergy-guided order set that was shown to increase appropriate antibiotic use from 47% to 85%.11 By guiding GBS test ordering, you can maximize the use of highly sensitive NAATs for all mothers, while identifying the few candidates for culture testing.

Laboratorians are well positioned to discuss the limitations of culture testing with physicians and champion the appropriate use of NAAT over culture. Consider how you can guide the discussion to bring new methods into your lab for more accurate antepartum screening.

Are you ready to champion the next level of GBS screening? Hologic® offers educational resources to help keep you up to speed. Visit us at Panther Fusion® GBS Assay.

    1. Taminato M, Fram D, Torloni MR, Belasco AG, Saconato H, Barbosa DA. Screening for group B Streptococcus in pregnant women: a systematic review and meta-analysis. Rev Lat Am Enfermagem. 2011;19(6):1470-1478. doi:10.1590/s0104-11692011000600026 2. Fay K, Almendras O, Robinson-Dunn B, Schrag S. Antenatal and Intrapartum Nucleic Acid Amplification Test Use for Group B Streptococcus Screening – United States 2016, J Diag Micro & Inf Dis 2019 Jun, vol 94:2; 157-159. 3. Centers for Disease Control and Prevention. Group B Strep (GBS): Fast Facts. Last Reviewed: October 18, 2022. Accessed June 6, 2023.,the%20bacteria%20late%20in%20pregnancy4. Seale AC, Blencowe H, Bianchi-Jassir F, et al. Stillbirth with Group B Streptococcus Disease Worldwide: Systematic Review and Meta-analyses. Clin Infect Dis. 2017;65(suppl_2):S125-S132. 5. Verani JR, McGee L, Schrag SJ; Division of Bacterial Diseases, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention (CDC). Prevention of perinatal group B streptococcal disease--revised guidelines from CDC, 2010. MMWR Recomm Rep. 2010;59(RR-10):1-36. Page 3 of PDF, col 1, para 4-col 2, para 1. 6. Filkins L, Hauser J, Robinson-Dunn B, Tibbetts R, Boyanton B, Revell P. Published 10 March 2020. Updated 23 July 2021. Guidelines for the Detection and Identification of Group B Streptococcus. American Society for Microbiology. Accessed June 6, 2023. 7. ACOG Committee Opinion. Prevention of Group B Streptococcal Early-Onset Disease in Newborns. Washington; DC: American College of Obstetricians and Gynecologists; 2019;134:319-40. No.797. 8. Shin JH and Pride DT. Comparison of Three Nucleic Acid Amplification Tests (NAATs) and Culture for Detection of Group B Streptococcus (GBS) from Enrichment Broth. J Clin Microbiology JCM.01958-18; DOI: 10.1128/JCM.01958-18 9. Centers for Disease Control and Prevention. Is it Really a Penicillin Allergy? Accessed June 6, 2023. 10. Esteve FC. Decline in GBS early onset disease rates is likely to continue. Accessed June 6, 2023. 11. Li LX, Oliver C, Ronzoni S, et al. Improving intrapartum group B Streptococcus prophylaxis in patients with a reported penicillin or cephalosporin allergy: a quality improvement project. J Obstetr Gynaecol Can 2022; 44:769–76.