Did you know that BV isn't a STI?

Did you know that BV isn't a STI?

December 2022

In this month's Did You Know? series, Chief Science Officer Beth DuPriest, PhD  explains the different disease states between BV and STIs, noting that epidemiological data suggests BV transmission, similar to STI transmission, may be driven by sexual activity.  Have a question about vaginal biome science? Submit yours here and your answer may be featured in an upcoming newsletter.

Q: Is BV similar to a sexually transmitted infection?

Bacterial vaginosis (BV) isn’t a sexually transmitted infection (STI)…but sometimes it acts like one. What makes something an STI? An STI follows the concept from germ theory that a single pathogen causes a single disease, and of course that the pathogen can only be acquired by sexual contact. If a woman is infected by Chlamydia trachomatis, she can expect to have a set of symptoms consistent with the disease we call chlamydia, though they may be mild. Trichomonas vaginalis infection causes similar but distinct symptoms. With both diseases – and other STIs – a positive test carries a high specificity and sensitivity for the presence of the causative organism. With an STI that follows germ theory, if you kill the pathogen, you cure the disease, and the disease cannot be passed on to anyone else. A test of cure, if done after treatment, would show the absence of the pathogen.

Although the exact mechanisms behind BV are still being determined, it is clear that BV is a polymicrobial condition, not a disease caused by a single pathogen. We don’t yet understand why some women have certain symptoms and others have different symptoms, or none at all. Although Gardnerella vaginalis was thought to be the cause of BV for decades, it is now clear that many healthy women can harbor large amounts of the bacteria without any symptoms at all. The same is true for many of the other species identified in BV, like Atopobium vaginae, Megasphaera, Mobiluncus curtisii, Prevotella bivia and others. We also don’t understand why antibiotics that kill these species fail to achieve clinical cure about 20% of the time, or why the condition recurs at such high rates (>40% in 3 months, ~70% within a year). These patterns are not consistent with a single pathogen-single disease theory, and as such, BV is not considered an STI.

That said, epidemiological data suggest that BV transmission in many ways is like an STI. BV is not observed in sexually inexperienced women and only rarely in those who have had only non-coital sexual experiences1. This suggests sex, or at least some kind of sexual contact, is required for acquisition of BV. In women who have sex with women, it is more likely a woman has BV if her partner also has BV2. BV is also correlated with other high-risk sexual practices such as having a new partner, having multiple partners, having sex without a barrier method of contraception, having a young age at sexual debut, and having sex frequently3. The challenge in clarifying the role of sexual contact in BV is that the kinds of experiments that would need to be done to verify sexual transmission of BV are unethical – it would be immoral to give patients BV intentionally – and there is no good animal model of BV, as humans are the only species with a Lactobacillus-dominant vaginal microbiome.

Unfortunately, the lack of clarity around the etiology of BV leads to inconsistent messaging and a sense for many women of shame and guilt surrounding their “contracting” BV3. Women with BV should be helped to understand that although sex may be a trigger for BV, BV is not an STI, and it is not their fault they have this condition. There is a delicate balance between empowering women to make healthy choices and making them feel responsible for getting BV. The artful healthcare practitioner will be able to help women understand how to take control of their health without making them feel ashamed or guilty for having what is the most common vaginal condition in the world.



1. Fethers KA, Fairley CK, Morton A, et al. Early Sexual Experiences and Risk Factors for Bacterial Vaginosis. J Infect Dis. 2009;200(11):1662-1670. doi:10.1086/648092

2. Marrazzo JM, Thomas KK, Fiedler TL, Ringwood K, Fredricks DN. Risks for acquisition of bacterial vaginosis among women who report sex with women: a cohort study. PloS One. 2010;5(6):e11139. doi:10.1371/journal.pone.0011139

3. Bilardi J, Walker S, Mooney-Somers J, et al. Women’s Views and Experiences of the Triggers for Onset of Bacterial Vaginosis and Exacerbating Factors Associated with Recurrence. PloS One. 2016;11(3):e0150272. doi:10.1371/journal.pone.0150272

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