Bacterial vaginosis independently associated with increased STI co-infection

Women who tested positive for bacterial vaginosis (BV) were more than 3 times as likely to also test positive for at least one nonviral sexually transmitted infection (STI) compared with BV-negative women, according to a retrospective cross-sectional study of more than 1.5 million women published in O&G Open, a peer-reviewed companion journal to Obstetrics & Gynecology.^1,2

The study, conducted by researchers at Quest Diagnostics and Hologic, Inc, analyzed deidentified aggregated laboratory data from women aged 15 years and older who underwent molecular testing for BV, vulvovaginal candidiasis (VVC), Chlamydia trachomatis, Neisseria gonorrhoeae, or Trichomonas vaginalis through Quest Diagnostics from 2022 to 2024, described as the largest national study of its kind.² A subset of more than 37,000 women also underwent molecular testing for Mycoplasma genitalium.¹

How prevalent was BV, and how often did coinfection occur?

Overall, BV and VVC positivity rates in the study population were 38.7% and 28.5%, respectively, with 10.8% of patients testing positive for both.^1,2 Among BV-positive women, 12.0% had at least one STI, compared with 3.8% of BV-negative women (P < .001). Specifically, 10.9% of BV-positive women had only one concurrent STI and 1.1% had 2 to 4 STIs, compared with 3.6% and 0.2% in the BV-negative group, respectively.¹

How strongly was BV associated with each STI?

After adjustment for age, geographic region, and VVC results, BV-positive status was significantly associated with increased odds of all 4 nonviral STIs evaluated (P < .001 for all):¹

• Chlamydia trachomatis: adjusted odds ratio (OR) 2.8 (95% CI, 2.8–2.9)
• Neisseria gonorrhoeae: OR 3.8 (95% CI, 3.6–4.0)
• Trichomonas vaginalis: OR 3.6 (95% CI, 3.6–3.7)
• Mycoplasma genitalium: OR 1.9 (95% CI, 1.8–2.1)

VVC status alone was not associated with increased risk of STI coinfection.^1,2

Study co-author Damian Alagia, III, MD, MS, MBA, FACS, comments on the findings below. In a recent interview with Contemporary OB/GYN, Alagia further discussed STI rates in women, including the follow-up gaps that remain in pregnant persons. Click here to watch.³

What do these findings mean for clinical practice?

Growing evidence suggests that changes in the vaginal microbiome may contribute not only to vaginitis but also to increased susceptibility to STIs including HIV, chlamydia, gonorrhea, and trichomonas.² Centers for Disease Control and Prevention guidelines recommend that women with BV be tested for STIs, which can present with overlapping symptoms that complicate diagnosis. Modern molecular diagnostics allow for comprehensive assessment of vaginal infections from a single specimen.

“This large study underscores the value of comprehensive molecular testing when clinically indicated, enabling clinicians to detect coinfections from a single specimen, optimize patient management, and strengthen evidence-based care,” added study co-author Elizabeth M. Marlowe, MS, PhD, Executive Director, Infectious Disease, Quest Diagnostics, in a statement.

The primary limitation of the study was its reliance on data from a single national laboratory, with specific patient-level risk factors not available for analysis.²

References:

1. Marlowe EM, Chen Z, Van K, et al. Concurrent STI risk in women with bacterial vaginosis or vulvovaginal candidiasis: a retrospective cross-sectional study of over 1.5 million women. O&G Open. 2024. doi:10.1097/og9.0000000000000185
2. Quest Diagnostics. Bacterial vaginosis linked to increased STI co-infection, finds national study of 1.5 million women from Quest Diagnostics. Press release. Published 2026.
3. Fitch J. Closing the STI screening and follow-up gap in pregnancy, with Damian Alagia, III, MD. Contemporary OB/GYN. Published July 23, 2026. Accessed July 30, 2026. https://www.contemporaryobgyn.net/view/closing-the-sti-screening-and-follow-up-gap-in-pregnancy-with-damian-alagia-iii-md