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Updated: Aug 16, 2026
A Murine Model of Group B Streptococcus Vaginal Colonization
Published on: November 16, 2016
Antenatal screening for Group B Streptococcus: a diagnostic cohort study
Janet E Hiller1, Helen M McDonald, Philip Darbyshire
1Department of Public Health, University of Adelaide, Adelaide, 5005, Australia. janet.hiller@adelaide.edu.au
Insights
Delaying Group B Streptococcal (GBS) screening until 36 weeks gestation improves detection of colonization. A single vaginal swab is as effective as combined swabs for GBS screening in pregnant women.
Area of Science:
- Obstetrics and Gynecology
- Infectious Diseases
- Microbiology
Background:
- Strategies to prevent early-onset Group B Streptococcal (GBS) sepsis are crucial.
- GBS infection is acquired vertically from mother to infant.
- Optimizing GBS screening timing and methods is essential for prevention.
Purpose of the Study:
- To establish scientific evidence for optimal GBS screening timing and methods in Australia.
- To compare the predictive value of GBS screening at 35-37 weeks versus 31-33 weeks gestation.
- To evaluate risk factor strategies and swab types (vaginal alone vs. combined vaginal/perianal) for GBS detection.
Main Methods:
- Women provided vaginal and perianal swabs at 31-33 weeks, 35-38 weeks, and during labor.
- Swabs were cultured using layered horse blood agar and selective broth.
- Test characteristics were calculated for different screening strategies and timings.
Main Results:
- A high-risk strategy was ineffective in predicting GBS status during labor.
- Delaying GBS screening until 36 weeks significantly improved the identification of colonized women.
- No clear advantage was found for combined vaginal and perianal swabs over vaginal swabs alone.
Conclusions:
- This study provides clear evidence for optimal GBS screening timing.
- Adding a perianal swab to vaginal swabs does not offer a significant benefit.
- Findings will aid communication between clinicians and pregnant women regarding GBS prevention.
Background:
A range of strategies have been adopted to prevent early onset Group B Streptococcal (EOGBS) sepsis, as a consequence of Group B Streptococcal (GBS) vertically acquired infection. This study was designed to provide a scientific basis for optimum timing and method of GBS screening in an Australian setting, to determine whether screening for GBS infection at 35-37 weeks gestation has better predictive values for colonisation at birth than screening at 31-33 weeks, to examine the test characteristics of a risk factor strategy and to determine the test characteristics of low vaginal swabs alone compared with a combination of perianal plus low vaginal swabs per colonisation during labour.
Methods:
Consented women received vaginal and perianal swabs at 31-33 weeks gestation, 35-38 weeks gestation and during labour. Swabs were cultured on layered horse blood agar and inoculated into selective broth prior to analysis. Test characteristics were calculated with exact confidence intervals for a high risk strategy and for antenatal screening at 31-33 and 35-37 weeks gestation for vaginal cultures alone, perianal cultures alone and combined low vaginal and perianal cultures.
Results:
The high risk strategy was not informative in predicting GBS status during labour. There is an unequivocal benefit for the identification of women colonised with GBS during labour associated with delaying screening until 36 weeks however the results for method of screening were less definitive with no clear advantage in using a combined low vaginal and perianal swabbing regimen over the use of a low vaginal swab alone.
Conclusion:
This study can contribute to the development of prevention strategies in that it provides clear evidence for optimal timing of swabs. The addition of a perianal swab does not confer clear benefit. The quantification of advantages and disadvantages provided in this study will facilitate communication with clinicians and pregnant women alike.
