Revisiting Bacterial Vaginosis: Evidence for Sexual Transmission and the Role of Partner Treatment in Reducing Recurrence

Bacterial vaginosis (BV) is the most common vaginal infection in women of reproductive age worldwide yet its pathogenesis, optimal treatment strategies, and effective prevention measures are still not fully understood. One of the most frustrating aspects of BV—for both patients and clinicians—is its high rate of recurrence: up to 50% of women will experience recurrence within 6 months.¹ This clinical pattern has raised important questions about whether sexual activity may be a contributing factor. While the association between BV and sexual activity is well-established, the complexity of the infection-- and historically negative results from partner treatment trials-- have made it difficult to define the precise role of sexual transmission in its etiology. However, results of a recent study published in the New England Journal of Medicine offers the strongest evidence to date that treating male partners of women with BV can significantly reduce recurrence.² These findings have led to calls to reclassify BV as a sexually transmitted infection (STI) but is there other evidence to support this perspective?

Burden and Recurrence

BV can cause distressing physical symptoms—including vaginal discharge and odor—and increases the risk of acquiring STIs, pelvic inflammatory disease and HIV. It is also associated with adverse reproductive outcomes, including pre-term birth, spontaneous abortion, and other obstetric and gynecologic complications. In the United States, BV affects an estimated 29% of women in the general population, with disproportionately higher prevalence among Black (52%) and Hispanic (32%) women compared to white women (23%).³ The high rate of recurrence means many women face repeated symptoms, frequent healthcare visits, multiple courses of antibiotics, and lost time from work. Beyond the physical symptoms, recurrent BV can significantly affect women’s sexual, emotional and social well-being.⁴

Vaginal microbiome and BV-associated bacteria

The vaginal microbiome is dynamic; normal fluctuations occur during the menstrual cycle, pregnancy, and throughout a woman’s life. When healthy, the vaginal microbiome is dominated by Lactobacillus, which produces antimicrobial compounds such as lactic-acid and hydrogen peroxide. In bacterial vaginosis, lactobacilli are replaced is replaced by high concentrations of anaerobic bacteria resulting in a disruption of the acidic environment and dysbiosis.

BV was first described in 1955 and initially attributed to a single bacterial pathogen, later named Gardnerella vaginalis.⁵ In the decades that followed, researchers observed that Gardnerella could also be found in the vaginal microbiota of women without BV. In fact, Gardnerella occurs in up to 70% of women without BV.⁶ At the same time, other microorganisms were increasingly detected in the vaginal flora of women with BV, leading to the recognition of BV as a polymicrobial infection. Advances in molecular diagnostics have identified many novel bacterial species associated with BV, substantially improving our understanding of its pathogenesis and improving diagnostic capabilities.⁶

Evidence of sexual transmission

In addition to clarifying the pathology of BV, molecular testing has provided key evidence supporting the sexual transmission of BV-associated bacteria. Modern genetic sequencing has allowed researchers to characterize the bacterial communities not only in the vagina, but also on the penis; BV-associated bacteria have been identified on the skin of the head of the penis and within the end of the male urethra.⁷ Moreover, studies of monogamous heterosexual couples have found strong concordance between the microbiota of women with recurrent BV and the penile microbiota of their male partners.⁸ Further support for transmissibility of BV comes from studies of same-sex female couples which show within-couple concordance for BV as well as specific BV-associated bacteria.⁹

Along with microbiologic findings, there is considerable evidence linking behavioral risk factors to BV. Increased number of sex partners, a new sex partner, and inconsistent use of condoms correlate with higher risk of BV and, conversely, consistent use of condoms is associated with decreased risk.¹⁰ Together these findings suggest that genital-genital contact, irrespective of gender, may facilitate the sexual transmission of BV.

The hypothesis that BV could be sexually transmitted emerged as soon as the condition was first identified. The researchers credited with discovering BV conducted studies in the 1950s to test this idea. They attempted to induce BV in ‘healthy’ women by transferring vaginal discharge from women with BV to fifteen women without BV and by inoculating other groups of women with fresh cultures of Gardnerella vaginalis. BV developed in 11/15 women who received vaginal discharge transferred from women with BV, whereas inoculation with G. vaginalis alone produced mixed results.¹⁰

Partner Treatment studies

If BV can be sexually transmitted, treating partners could theoretically reduce reinfection and recurrence. Six studies in the 1980s and 1990s evaluated whether treating male partners with oral antibiotics could reduce recurrence rates in women with BV, but none demonstrated a clear benefit. However, these trials had many limitations including small sample sizes, inconsistent diagnostic criteria, varied antibiotic regimens, lack of adherence data, and high attrition.¹⁰ A more rigorous randomized controlled trial in 2021 also showed no overall benefit of oral partner treatment, although secondary analysis suggested some effect in women whose male partners were 100% adherent to the treatment regimen.^10,11

NEW Partner Treatment Evidence/ NEJM study

Recently, in the New England Journal of Medicine, Vodstrcil et al. published the results of the first RCT of male partner treatment with simultaneous oral AND topical antibiotics to prevent BV recurrence. Unlike prior partner treatment studies, a significant benefit was found; recurrence of BV was 35% when male partners of women with BV were treated vs 63% in women whose partners did not receive treatment.²  These results corresponded to 2.6 fewer episodes of recurrent BV per year for women whose partners were also treated. An accompanying editorial emphasized the significance of the findings; these results provide definitive actionable evidence that BV-associated bacteria can be sexually transmitted.¹²

While promising, the results of the study may not apply to every woman with recurrent BV. The couples who enrolled in the study were monogamous; treatment of male partners may not be effective in couples where one or both partners have sex with other people. The study population was small and represented racial and ethnic groups specific to Australia, where the trial took place. In addition, most men were uncircumcised, and more than a quarter of the women used IUDs, both factors that are associated with higher rates of BV and recurrent BV.²  

In addition, 35% of women whose partners were treated still experienced recurrent infections. While the evidence is clear that BV-associated bacteria can be sexually transmitted, there is also substantial evidence that other factors may also contribute to the recurrence of BV in some women and/or recurrence may be multifactorial. The persistence of a BV-associated biofilm, failure of recolonization of the vagina with lactobacilli, and variations in immune response may also contribute to the likelihood of recurrence.¹⁰  

A paradigm shift 

The recent study findings are highly significant and signal a potential shift in how clinicians approach the treatment of recurrent BV and how they counsel patients about the role of sexual transmission. Most notably, the results underscore the need to acknowledge the role of male partners in recurrent BV and to involve them in treatment strategies.  This will require men to accept responsibility for their contribution to recurrent infections and commit to an intensive treatment regimen for the benefit of their partners. In the study, 14% of the men reported taking less than 70% of their doses of medication, indicating that adherence for men may be a challenge.² Still, these findings offer renewed hope for women who have until now had limited options for managing recurrent BV. 

This shift in management strategy also elevates the importance of timely and accurate diagnosis. Advances in molecular testing now allow for precise and rapid identification of specific BV-associated bacteria. These tests offer improved sensitivity and specificity over traditional methods for the diagnosis of BV and enable clinicians to make informed decisions at the point of care.^13,14 As new treatment approaches emerge for recurrent BV—especially those involving partner management—accurate and timely diagnosis becomes essential to ensure appropriate treatment for both patients, and when indicated, their partners.