For decades, bacterial vaginosis (BV) was explained to women as an imbalance in their vaginal flora, a frustrating condition they had to manage alone. Groundbreaking new research has fundamentally overturned that view, providing compelling evidence that BV is, in fact, sexually transmitted.
A Paradigm Shift Backed by New Data
The transformation in understanding stems from a pivotal Australian study published in the New England Journal of Medicine. The trial involved 150 heterosexual couples and found that treating male partners alongside women with BV dramatically improved outcomes. When men received a specific dual therapy—oral metronidazole and a topical clindamycin cream applied to the penile skin—the recurrence rate for women within 12 weeks was halved, falling to 35% compared to 63% for women whose partners were untreated. The results were so compelling the trial was stopped early.
This study provided what Professor Jack Sobel, an infectious disease specialist at Wayne State University, called a “smoking gun” for BV being a sexually transmitted disease. He noted that the International Society for the Study of Vulvovaginal Disease now officially endorses selective male partner treatment.
Why Treating the Partner is Now Seen as Crucial
The Australian trial’s success, where previous attempts in the 1980s and 1990s had failed, hinges on a critical detail: the treatment regimen. Earlier studies gave men only oral antibiotics, which proved ineffective. The new protocol combines oral medication with a topical cream, targeting harmful bacterial biofilms that can colonise penile skin. This dual approach addresses a key reason for scepticism in the past—the lack of a single causative bacterium. Experts like Dr Phillip Hay, a sexual health consultant at Guy’s and St Thomas’ Hospital in London, explain that BV appears to be caused by a consortium of bacteria, such as Gardnerella vaginalis and Mobiluncus species, which work together. “Some of the bacteria produce molecules which are substrate for other ones to grow,” said Dr Hay.
The new understanding posits that while factors like a lack of protective Lactobacillus bacteria in the vagina may make recurrence more likely, the initial colonisation by the “wrong” bacteria is typically passed on during sex. Treating only the woman reduces the harmful bacteria temporarily, but if her partner harbours the same complex bacterial community, reinfection is highly probable. This explains why BV, which causes discharge and a distressing odour and affects up to a third of women, has been so notoriously difficult to cure with antibiotics given to women alone.
The UK’s Gradual Path to Change
While guidelines in the United States and Australia have already changed to advise partner treatment, the UK’s national health bodies are moving more slowly. The British Association for Sexual Health and HIV (BASHH) is currently updating its clinical guidelines, which have not been revised since 2012. Dr Sarah Flew, the guideline editor, confirmed that BASHH considers the full range of available evidence and the update is likely to be released this year.
Some UK clinicians are not waiting. Dr Phillip Hay is among those already prescribing for male partners and helping to rewrite his hospital’s local guidelines. “Guidelines are minimal standard of treatment for people who don’t really know the disease area – if you do, you try and follow the research as it comes out,” he said. However, he notes that General Practitioners, who treat many women with BV, are more likely to follow the National Institute for Health and Care Excellence (NICE) evidence summary, which currently makes no mention of treating men. A NICE spokesperson said they are aware of the new research and would consider it, along with any updated BASHH guidance, in a future review.
The scale of the issue underscores the need for effective treatment. In the UK, an estimated 3.4 million women aged 15 and over are affected by BV, with nearly 1.9 million suffering from recurrent cases. Beyond the immediate symptoms, BV carries significant health risks, including increased susceptibility to sexually transmitted infections like HIV, chlamydia and gonorrhoea, and is linked to pelvic inflammatory disease, infertility, and adverse pregnancy outcomes such as preterm birth and miscarriage.
The recognition of BV as sexually transmitted also sheds light on its prevalence in other groups. Research indicates lesbian women have a 2.5-fold increased likelihood of BV compared to heterosexual women, with high concordance of vaginal flora within partnerships supporting the concept of sexual transmission. For pregnant women, symptomatic BV is associated with risks of premature birth and miscarriage, and treatment is recommended.
As the medical community assimilates this shift, ongoing research is exploring partner treatment in LGBTQIA+ couples and alternative therapies like probiotics to restore healthy vaginal bacteria. The cost of treating male partners is considered relatively low, but for now, the definitive step change rests on a new, shared understanding of responsibility for a very common infection.