Reference: N Engl J Med. 2025 Mar 6;392(10):947-957
Practice Point: A practice-changing study shows that treating male partners with oral AND topical antimicrobials cuts bacterial vaginosis (BV) recurrence rates by half, (finally) confirming BV’s status as an STI.
EBM Pearl: The whole point of randomization is to make sure that variables that would have otherwise affected the outcome are equally represented among treatment groups such that the only possible causal association is the intervention in question.
Despite BV being the most common cause of vaginal discharge in females of reproductive age, with a nearly 60% 1-year recurrence rate, its status as an STI has been debated for years. Naysayers have cited the lack of one clear pathologic mechanism, the lack of a similar disease process in men, and the lack of efficacy with treating male partners with metronidazole as reasons to put the STI issue to bed, so to speak. Even the CDC does not currently recommend routine treatment of male partners (as of 2021), despite lengthy discussions in its recommendation statement about how it maybe kinda could possibly be an STI. But let’s be honest—if a quarter of the male population were affected by recurrent, foul-smelling genital discharge despite repeat courses of messy creams or pills that made their mouths taste like metal and required avoidance of alcohol for 7 days, there’s a good chance we’d have figured this out by now. Well, leave it to a team of researchers led by a woman to finally get to the bottom of this.
These Australian authors designed a high-quality, open-label, randomized controlled trial of 164 adult heterosexual monogamous couples in which the female partner had symptomatic BV to evaluate the impact of treating male partners with oral and topical antimicrobials on BV recurrence. 87% of the female partners had had BV in the past, with a median of 3 previous infections. In all couples, the female partner received first-line treatment with metronidazole 400 mg orally twice daily for 7 days or, if contraindicated, clindamycin 2% cream intravaginally for 7 nights or metronidazole 0.75% intravaginally for 5 nights. Male partners were randomized to receive either no treatment or a 7-day course of metronidazole 400 mg twice daily and clindamycin 2% cream applied topically to the penile skin. While the couples were not blinded, all outcome assessors were. All couples were told not to have any sexual contact during the treatment courses.
The results were impressive. So impressive, in fact, that the trial was terminated early for efficacy at the first interim analysis after only 150 couples had completed the 12-week follow-up. In a modified intention-to-treat analysis, BV recurrence rates at 12 weeks were 35% in the male partner treatment group compared to 63% in the untreated group. That’s an NNT of 4, with an absolute risk difference of -2.6 recurrences per person-year.
The study was not perfect, but because of our old trusty pal randomization, the effects of what could have otherwise been confounders are minimal. For instance, 80% of the male partners were uncircumcised and about 30% of the female partners had IUDs in place, both of which predispose to bacteria carriage. However, because patients were randomly distributed among the treatment groups and analyzed by intention to treat, prognostic equivalence was maintained, and these factors do not put the causal association between treatment of male partners and BV recurrence in question, as affirmed by results of subgroup analyses stratified by these factors. One limitation of the study is that it included mostly people of Western Pacific and European backgrounds, which may limit generalizability among ethnic groups with documented higher prevalence of BV. Also, all of the couples were in monogamous relationships, so we can’t draw conclusions about the efficacy of treating male partners for non-coupled transmission. (Yet.)
The bottom line, however, is that we are witnessing a paradigm shift: BV should henceforth be considered an STI and male partners should be treated. As with chlamydia, gonorrhea, and other curable STIs, treatment of BV should be a two-for-one deal. Just make sure the male partner gets BOTH topical and oral antibiotics.
For more information, see the topic Bacterial Vaginosis (BV) in DynaMed.
DynaMed EBM Focus Editorial Team
This EBM Focus was written by Katharine DeGeorge, MD, MS, Senior Deputy Editor at DynaMed and Associate Professor of Family Medicine at the University of Virginia. Edited by Alan Ehrlich, MD, FAAFP, Executive Editor at DynaMed and Associate Professor in Family Medicine at the University of Massachusetts Medical School; Dan Randall, MD, MPH, FACP, Senior Deputy Editor at DynaMed; McKenzie Ferguson, PharmD, BCPS, Senior Clinical Writer at DynaMed; Rich Lamkin, MPH, MPAS, PA-C, Clinical Writer at DynaMed; Matthew Lavoie, BA, Senior Medical Copyeditor at DynaMed; Hannah Ekeh, MA, Senior Associate Editor II at DynaMed; and Jennifer Wallace, BA, Senior Associate Editor at DynaMed.