In a new research study published this month in the New England Journal of Medicine, researchers out of Australia’s Monash University report that treating a woman’s male partner too can assist in beating recurring bacterial vaginosis.
For many women, boomeranging bacterial vaginosis is an ongoing bugbear; in more than half of cases it comes back within six months. In an open-label trial conducted over four years, Melbourne-based researchers tested whether giving men a course of antimicrobials at the same time their partners were being treated, could keep bacterial vaginosis from returning within twelve weeks.
The team found that a combination of metronidazole pills and a course of topical clindamycin cream on the didgeridoo slashed bacterial vaginosis recurrence to half of that of women whose partners weren’t treated. In fact, this intervention was so effective that halfway through the trial, the data and safety monitoring board brought it to a halt. The mid-point analysis showed that the treatment worked so well that continuing was unfair to the women in the control group.
Stepping Up
So what do male partners have to do with bacterial vaginosis? Dr Lenka Vodstrcil the lead investigator explained to MNB that women in a relationship with the same mate before, during and after treatment for bacterial vaginosis, are two to three times more likely to experience another recurrence. Sex involves contact at the closest quarters, so it’s inevitable that without barrier method contraception, for example condoms, partners will exchange some of their microbiome along with their sweet nothings. Researchers have long suspected that couples could be reinfecting each other.
When doctors took a more in depth look to see whether men also carry the bacterial vaginosis bugs, they discovered them hiding out in the urethra and on the penis’s skin. Close inspection of the DNA profiles of these microbes revealed that not only can men pick up bacterial vaginosis bacteria, when they do, they have the same ones as their partner. Women in same-sex relationships also share vaginal microbial profiles. Talk about what’s mine is yours!
Unfortunately while treating both partners is standard practice for sexually transmitted infections, currently, only women are treated for bacterial vaginosis. Vodstrcil and her colleagues realized that inviting men to step up and get treated could be to key to keeping bacterial vaginosis away. Researchers have tried to treat men with oral antibiotics over the years, but without much success. This time, however, they were armed with more information about how microbes hide out in men’s nooks and crannies. It turns out that women with circumcised male partners are less likely to experience bacterial vaginosis. The team wondered whether using an antimicrobial ointment on the penis, paired with oral antimicrobials could be the solution?
Sharing the Load
Between 2019 and 2023, the researchers, recruited 164 heterosexual couples across three states for the study. In order to qualify for the trial, women had to have been diagnosed with symptomatic bacterial vaginosis. She must be over 18 years of age and be in a monogamous sexual relationship with a man for a minimum of eight weeks before the trial. She should be undergoing an antimicrobial treatment for her bacterial vaginosis. The pairs were randomized and split into two groups, the experimental group and age control group.
Participants assigned to the control group got the standard of care treatment for bacterial vaginosis. That is, the female partner was treated with 400 mg oral metronidazole twice daily for 7 days (alternatively intravaginal 2% clindamycin cream for seven nights or intravaginal 0.75% metronidazole gel for five nights if metronidazole tablets were contraindicated). Men received no treatment.
Treats for My Treats
In the treatment group, women got the same treatment as those in the control group. This time, however, their partners also used 400 mg oral metronidazole twice per day for seven days, and applied a 2 cm blob of 2% clindamycin cream to their glans penis and upper shaft twice a day for seven days. The partners were asked to use their medicine in the same seven-day period to make sure they were coordinating their treatment. For the next twelve weeks, women visited the clinic at four-week intervals to be tested for bacterial vaginosis and to hand in questionnaires about symptoms and adherence during the interval between visits. Men were also asked to fill in questionnaires at the beginning and end.
This trial was randomized, and used controls, but did not feature a placebo control. Sometimes placebo-controlled trials are not the right type of study to answer the questions you are posing. For example, when comparing a new treatment to an established one to see if it is an improvement – a placebo is unnecessary. Or, in some circumstances, the placebo can scupper the results. In this case using a placebo ointment could interfere with the microbial flora living on the penis. There are all sorts of ways the cream itself could frustrate the outcomes by supporting growth of other types of microbes or killing off pathogens.
Beating Recurring Bacterial Vaginosis
Out of the 164 couples, 27 had changes in circumstances that made them ineligible to take part, didn’t stick to the medication regimen or dropped out before the end of the trial. The two arms of the trial were the control group, 68 couples and the partner-treatment group, 69 couples.
The results of the primary analysis showed that at the end of the experiment, 43 of 68 women in the control group suffered a recurrence of bacterial vaginosis within twelve weeks of starting the study. These 43 women, on average experienced 4.2 infections per person years. In the treatment group, however, only 24 out of 69 suffered from a relapse and those women had fewer recurrences – on average only 1.1 additional infections per person year.
Women in the treatment group who had a recurrence of bacterial vaginosis had a longer interval between treatment and reinfection than women in the control group, buying an extra 19 days.
All in all treating men with both oral and topical antimicrobials almost halved the number of women who had a recurring infection. Those women who did experience a relapse had one quarter of the number of infections if their man was diligent about applying his cream and taking his meds than the women whose partners did not get treated.
Second Pass
Secondary and sensitivity analysis of the data confirmed that treating male partners at the same time as a bacterial vaginosis patient cuts both the absolute chance of recurrence and the frequency of recurrences.
The sensitivity analysis showed that the lowest recurrence rate (1.3 per patient year) was achieved by men who stuck to the regime and took all their doses.
They also looked to see whether known risk factors for bacterial vaginosis contributed to recurrence. Amongst women whose partners got treated, there was no statistically significant difference between women who had an IUD and those who didn’t. Similarly the men’s circumcision status did not make any difference.
A Problem Shared Is a Problem Halved
Men’s willingness to step up and help their partner was a key aspect of the success of this trial. Indeed, Dr Vodstrcil shared that she and her team were pleasantly surprised by the men’s commitment to helping their beloved bust the recurring bacterial vaginosis beat.
She explained that in the past, recruiting male partners for clinical trials had been tricky. Generally, men had been reluctant to join if they themselves didn’t have symptoms.
In this case, however, the fellas were highly motivated and willing to put up with a week of treatment if it meant their partner would get better. In an encouraging turn, she says, some men even sought out the trial website themselves and volunteered to take part. The men who participated put their best foot forward and diligently stuck to the treatment plan.
Bacterial Vaginosis in Brief
Bacterial vaginosis is the result of an imbalance in the types of bacteria that live in vaginas (the vaginal microbiome). Lactobacilli are friendly bacteria that help our bodies to defend themselves against other, less pleasant bugs. The lactobacilli produce germ busting lactic acid and hydrogen peroxide that keep the pH of the vagina acidic.
This acidic environment created by the lactobacilli kills off microbes that cause disease, protecting the vagina from invading yeast, bacteria and viruses. When something happens that causes a woman’s vaginal lactobacilli to die off it gives other bacteria the chance to take charge. Some women might get an itchy yeast over growth as Candida albicans takes its chance. Other women might experience an over growth of Gardnerella bacteria. Bacterial vaginosis is most often due to over growth of Gardnerella vaginalis bacteria.
When Gardnerella family bacteria bump lactobacilli off the top spot, they shift the pH making it more alkaline. This makes the vagina lose its protection from a host bacterial species. Bacterial species such as Dialister, Prevotell bivia, Parvimonas, Megasphaera, Peptostreptococcus, and Veillonella spp get in on the action, colonizing the vulva and vagina. These bugs pump out fishy smelling bio-amines that cause that tell-tale bacterial vaginosis odour.
Microbiome in The Balance
The Gardnerella overgrowth out competes lactobacilli for resources preventing them from making a come back. Not only does this bacterial over growth result is an unpleasant smell and grey/green watery discharge, but it makes you more susceptible to sexually transmitted infections and increases your risk of pelvic inflammatory disease.
Usually the lactobacilli help us to defend against germs that cause infections like chlamydia and gonorrhoea, but when the pH in a vagina starts to rise, it’s a lot easier for pathogens to flourish.
Researchers are not sure exactly what triggers the chain reaction that causes Gardnerella vaginalis overgrowth and bacterial vaginosis. Bacterial vaginosis is more common in women who are sexually active and doctors have noticed that it happens more often in women who have sex without condoms, use vaginal douches or have multiple partners.
The Source of Recurring Bacterial Vaginosis?
While epidemiologists say that bacterial vaginosis follows the same patterns as sexually transmitted infections, Gardnerella vaginalis also turns up in women who don’t have bacterial vaginosis and in women who have never had sex. What’s more, bacterial vaginosis can, although rarely, hit women and girls of all ages, whether or not they have ever had sex or sexual contact. However, sexual transmission does play a major part in the majority of cases. So where does the infection come from? How come some women have it and some don’t?
More recent research led investigators to use genetic testing on bacterial vaginosis swabs to identify what other types of microbe might be present. It turns out that different combinations of bacteria work together to take over the vagina and there are more varieties of Gardnerella vaginalis than scientists realized.
If you just have regular Gardnerella vaginalis hanging out, unless you have some kind of interference for example using a vaginal douche, your microbes will usually be in balance. But if some a more virulent strain of Gardnerella vaginalis makes it into the vagina, it will join forces with the other pathogenic bugs hanging out in low numbers and overwhelm the lactobacilli. Breaking the bacterial back and forth is the key to preventing recurring bacterial vaginosis.
Some members of the Gardnerella vaginalis are more troublesome than others and may take more time to treat. Remember, while bacterial vaginosis germs can be passed to-and-fro it doesn’t mean that one partner or the other is to blame.
It Takes Two
The results of this study indicate that men can indeed transmit an infectious agent to their partners in cases of recurring bacterial vaginosis. It turns out that oral antibiotics are not enough, topical antimicrobials need to be applied to his penis to root out the hold outs.
The Monash team found that this simple intervention is very effective at preventing recurring infections. Vodstrcil says, ‘Our trial found that reinfection from an ongoing sexual partner is a significant driver of BV recurrence, and by adding male partner-treatment to the treatment of women, we now have a simple strategy to reduce BV recurrence.
This strategy would most likely benefit women in a monogamous relationship where both partners are able to be treated simultaneously. It is important to emphasize that couples avoid sexual contact until both had completed treatment, and that they are counselled to take all of the prescribed medication – the female partners of men who reported taking all of the doses of both treatments had the lowest rate of recurrence, indicating that adherence is important.’
For more information about this novel treatment plan for recurring bacterial vaginosis please visit https://www.mshc.org.au/sexual-health/bacterial-vaginosis.
Bibliography
Boris S, Barbés C. Role played by lactobacilli in controlling the population of vaginal pathogens. Microbes and Infection. 2000;2(5):543-546. doi:10.1016/S1286-4579(00)00313-0
CDC. About Bacterial Vaginosis (BV). Bacterial Vaginosis (BV). December 3, 2024. Accessed March 24, 2025. https://www.cdc.gov/bacterial-vaginosis/about/index.html
Muzny CA, Taylor CM, Swords WE, et al. An Updated Conceptual Model on the Pathogenesis of Bacterial Vaginosis. J Infect Dis. 2019;220(9):1399-1405. doi:10.1093/infdis/jiz342
Nelson TM, Borgogna JLC, Brotman RM, Ravel J, Walk ST, Yeoman CJ. Vaginal biogenic amines: biomarkers of bacterial vaginosis or precursors to vaginal dysbiosis? Front Physiol. 2015;6:253. doi:10.3389/fphys.2015.00253
Papanikolaou EG, Tsanadis G, Dalkalitsis N, Lolis D. Recurrent bacterial vaginosis in a virgin adolescent: a new method of treatment. Infection. 2002;30(6):403-404. doi:10.1007/s15010-002-2001-9
Shvartsman E, Hill JE, Sandstrom P, MacDonald KS. Gardnerella Revisited: Species Heterogeneity, Virulence Factors, Mucosal Immune Responses, and Contributions to Bacterial Vaginosis. Infect Immun. 2023;91(5):e0039022. doi:10.1128/iai.00390-22
Valenti P, Rosa L, Capobianco D, et al. Role of Lactobacilli and Lactoferrin in the Mucosal Cervicovaginal Defense. Front Immunol. 2018;9:376. doi:10.3389/fimmu.2018.00376
Vodstrcil LA, Plummer EL, Fairley CK, et al. Male-Partner Treatment to Prevent Recurrence of Bacterial Vaginosis. New England Journal of Medicine. 2025;392(10):947-957. doi:10.1056/NEJMoa2405404
In a new research study published this month in the New England Journal of Medicine, researchers out of Australia’s Monash University report that treating a woman’s male partner too can assist in beating recurring bacterial vaginosis.
For many women, boomeranging bacterial vaginosis is an ongoing bugbear; in more than half of cases it comes back within six months. In an open-label trial conducted over four years, Melbourne-based researchers tested whether giving men a course of antimicrobials at the same time their partners were being treated, could keep bacterial vaginosis from returning within twelve weeks.
The team found that a combination of metronidazole pills and a course of topical clindamycin cream on the didgeridoo slashed bacterial vaginosis recurrence to half of that of women whose partners weren’t treated. In fact, this intervention was so effective that halfway through the trial, the data and safety monitoring board brought it to a halt. The mid-point analysis showed that the treatment worked so well that continuing was unfair to the women in the control group.
Stepping Up
So what do male partners have to do with bacterial vaginosis? Dr Lenka Vodstrcil the lead investigator explained to MNB that women in a relationship with the same mate before, during and after treatment for bacterial vaginosis, are two to three times more likely to experience another recurrence. Sex involves contact at the closest quarters, so it’s inevitable that without barrier method contraception, for example condoms, partners will exchange some of their microbiome along with their sweet nothings. Researchers have long suspected that couples could be reinfecting each other.
When doctors took a more in depth look to see whether men also carry the bacterial vaginosis bugs, they discovered them hiding out in the urethra and on the penis’s skin. Close inspection of the DNA profiles of these microbes revealed that not only can men pick up bacterial vaginosis bacteria, when they do, they have the same ones as their partner. Women in same-sex relationships also share vaginal microbial profiles. Talk about what’s mine is yours!
Unfortunately while treating both partners is standard practice for sexually transmitted infections, currently, only women are treated for bacterial vaginosis. Vodstrcil and her colleagues realized that inviting men to step up and get treated could be to key to keeping bacterial vaginosis away. Researchers have tried to treat men with oral antibiotics over the years, but without much success. This time, however, they were armed with more information about how microbes hide out in men’s nooks and crannies. It turns out that women with circumcised male partners are less likely to experience bacterial vaginosis. The team wondered whether using an antimicrobial ointment on the penis, paired with oral antimicrobials could be the solution?
Sharing the Load
Between 2019 and 2023, the researchers, recruited 164 heterosexual couples across three states for the study. In order to qualify for the trial, women had to have been diagnosed with symptomatic bacterial vaginosis. She must be over 18 years of age and be in a monogamous sexual relationship with a man for a minimum of eight weeks before the trial. She should be undergoing an antimicrobial treatment for her bacterial vaginosis. The pairs were randomized and split into two groups, the experimental group and age control group.
Participants assigned to the control group got the standard of care treatment for bacterial vaginosis. That is, the female partner was treated with 400 mg oral metronidazole twice daily for 7 days (alternatively intravaginal 2% clindamycin cream for seven nights or intravaginal 0.75% metronidazole gel for five nights if metronidazole tablets were contraindicated). Men received no treatment.
Treats for My Treats
In the treatment group, women got the same treatment as those in the control group. This time, however, their partners also used 400 mg oral metronidazole twice per day for seven days, and applied a 2 cm blob of 2% clindamycin cream to their glans penis and upper shaft twice a day for seven days. The partners were asked to use their medicine in the same seven-day period to make sure they were coordinating their treatment. For the next twelve weeks, women visited the clinic at four-week intervals to be tested for bacterial vaginosis and to hand in questionnaires about symptoms and adherence during the interval between visits. Men were also asked to fill in questionnaires at the beginning and end.
This trial was randomized, and used controls, but did not feature a placebo control. Sometimes placebo-controlled trials are not the right type of study to answer the questions you are posing. For example, when comparing a new treatment to an established one to see if it is an improvement – a placebo is unnecessary. Or, in some circumstances, the placebo can scupper the results. In this case using a placebo ointment could interfere with the microbial flora living on the penis. There are all sorts of ways the cream itself could frustrate the outcomes by supporting growth of other types of microbes or killing off pathogens.
Beating Recurring Bacterial Vaginosis
Out of the 164 couples, 27 had changes in circumstances that made them ineligible to take part, didn’t stick to the medication regimen or dropped out before the end of the trial. The two arms of the trial were the control group, 68 couples and the partner-treatment group, 69 couples.
The results of the primary analysis showed that at the end of the experiment, 43 of 68 women in the control group suffered a recurrence of bacterial vaginosis within twelve weeks of starting the study. These 43 women, on average experienced 4.2 infections per person years. In the treatment group, however, only 24 out of 69 suffered from a relapse and those women had fewer recurrences – on average only 1.1 additional infections per person year.
Women in the treatment group who had a recurrence of bacterial vaginosis had a longer interval between treatment and reinfection than women in the control group, buying an extra 19 days.
All in all treating men with both oral and topical antimicrobials almost halved the number of women who had a recurring infection. Those women who did experience a relapse had one quarter of the number of infections if their man was diligent about applying his cream and taking his meds than the women whose partners did not get treated.
Second Pass
Secondary and sensitivity analysis of the data confirmed that treating male partners at the same time as a bacterial vaginosis patient cuts both the absolute chance of recurrence and the frequency of recurrences.
The sensitivity analysis showed that the lowest recurrence rate (1.3 per patient year) was achieved by men who stuck to the regime and took all their doses.
They also looked to see whether known risk factors for bacterial vaginosis contributed to recurrence. Amongst women whose partners got treated, there was no statistically significant difference between women who had an IUD and those who didn’t. Similarly the men’s circumcision status did not make any difference.
A Problem Shared Is a Problem Halved
Men’s willingness to step up and help their partner was a key aspect of the success of this trial. Indeed, Dr Vodstrcil shared that she and her team were pleasantly surprised by the men’s commitment to helping their beloved bust the recurring bacterial vaginosis beat.
She explained that in the past, recruiting male partners for clinical trials had been tricky. Generally, men had been reluctant to join if they themselves didn’t have symptoms.
In this case, however, the fellas were highly motivated and willing to put up with a week of treatment if it meant their partner would get better. In an encouraging turn, she says, some men even sought out the trial website themselves and volunteered to take part. The men who participated put their best foot forward and diligently stuck to the treatment plan.
Bacterial Vaginosis in Brief
Bacterial vaginosis is the result of an imbalance in the types of bacteria that live in vaginas (the vaginal microbiome). Lactobacilli are friendly bacteria that help our bodies to defend themselves against other, less pleasant bugs. The lactobacilli produce germ busting lactic acid and hydrogen peroxide that keep the pH of the vagina acidic.
This acidic environment created by the lactobacilli kills off microbes that cause disease, protecting the vagina from invading yeast, bacteria and viruses. When something happens that causes a woman’s vaginal lactobacilli to die off it gives other bacteria the chance to take charge. Some women might get an itchy yeast over growth as Candida albicans takes its chance. Other women might experience an over growth of Gardnerella bacteria. Bacterial vaginosis is most often due to over growth of Gardnerella vaginalis bacteria.
When Gardnerella family bacteria bump lactobacilli off the top spot, they shift the pH making it more alkaline. This makes the vagina lose its protection from a host bacterial species. Bacterial species such as Dialister, Prevotell bivia, Parvimonas, Megasphaera, Peptostreptococcus, and Veillonella spp get in on the action, colonizing the vulva and vagina. These bugs pump out fishy smelling bio-amines that cause that tell-tale bacterial vaginosis odour.
Microbiome in The Balance
The Gardnerella overgrowth out competes lactobacilli for resources preventing them from making a come back. Not only does this bacterial over growth result is an unpleasant smell and grey/green watery discharge, but it makes you more susceptible to sexually transmitted infections and increases your risk of pelvic inflammatory disease.
Usually the lactobacilli help us to defend against germs that cause infections like chlamydia and gonorrhoea, but when the pH in a vagina starts to rise, it’s a lot easier for pathogens to flourish.
Researchers are not sure exactly what triggers the chain reaction that causes Gardnerella vaginalis overgrowth and bacterial vaginosis. Bacterial vaginosis is more common in women who are sexually active and doctors have noticed that it happens more often in women who have sex without condoms, use vaginal douches or have multiple partners.
The Source of Recurring Bacterial Vaginosis?
While epidemiologists say that bacterial vaginosis follows the same patterns as sexually transmitted infections, Gardnerella vaginalis also turns up in women who don’t have bacterial vaginosis and in women who have never had sex. What’s more, bacterial vaginosis can, although rarely, hit women and girls of all ages, whether or not they have ever had sex or sexual contact. However, sexual transmission does play a major part in the majority of cases. So where does the infection come from? How come some women have it and some don’t?
More recent research led investigators to use genetic testing on bacterial vaginosis swabs to identify what other types of microbe might be present. It turns out that different combinations of bacteria work together to take over the vagina and there are more varieties of Gardnerella vaginalis than scientists realized.
If you just have regular Gardnerella vaginalis hanging out, unless you have some kind of interference for example using a vaginal douche, your microbes will usually be in balance. But if some a more virulent strain of Gardnerella vaginalis makes it into the vagina, it will join forces with the other pathogenic bugs hanging out in low numbers and overwhelm the lactobacilli. Breaking the bacterial back and forth is the key to preventing recurring bacterial vaginosis.
Some members of the Gardnerella vaginalis are more troublesome than others and may take more time to treat. Remember, while bacterial vaginosis germs can be passed to-and-fro it doesn’t mean that one partner or the other is to blame.
It Takes Two
The results of this study indicate that men can indeed transmit an infectious agent to their partners in cases of recurring bacterial vaginosis. It turns out that oral antibiotics are not enough, topical antimicrobials need to be applied to his penis to root out the hold outs.
The Monash team found that this simple intervention is very effective at preventing recurring infections. Vodstrcil says, ‘Our trial found that reinfection from an ongoing sexual partner is a significant driver of BV recurrence, and by adding male partner-treatment to the treatment of women, we now have a simple strategy to reduce BV recurrence.
This strategy would most likely benefit women in a monogamous relationship where both partners are able to be treated simultaneously. It is important to emphasize that couples avoid sexual contact until both had completed treatment, and that they are counselled to take all of the prescribed medication – the female partners of men who reported taking all of the doses of both treatments had the lowest rate of recurrence, indicating that adherence is important.’
For more information about this novel treatment plan for recurring bacterial vaginosis please visit https://www.mshc.org.au/sexual-health/bacterial-vaginosis.
Bibliography
Boris S, Barbés C. Role played by lactobacilli in controlling the population of vaginal pathogens. Microbes and Infection. 2000;2(5):543-546. doi:10.1016/S1286-4579(00)00313-0
CDC. About Bacterial Vaginosis (BV). Bacterial Vaginosis (BV). December 3, 2024. Accessed March 24, 2025. https://www.cdc.gov/bacterial-vaginosis/about/index.html
Muzny CA, Taylor CM, Swords WE, et al. An Updated Conceptual Model on the Pathogenesis of Bacterial Vaginosis. J Infect Dis. 2019;220(9):1399-1405. doi:10.1093/infdis/jiz342
Nelson TM, Borgogna JLC, Brotman RM, Ravel J, Walk ST, Yeoman CJ. Vaginal biogenic amines: biomarkers of bacterial vaginosis or precursors to vaginal dysbiosis? Front Physiol. 2015;6:253. doi:10.3389/fphys.2015.00253
Papanikolaou EG, Tsanadis G, Dalkalitsis N, Lolis D. Recurrent bacterial vaginosis in a virgin adolescent: a new method of treatment. Infection. 2002;30(6):403-404. doi:10.1007/s15010-002-2001-9
Shvartsman E, Hill JE, Sandstrom P, MacDonald KS. Gardnerella Revisited: Species Heterogeneity, Virulence Factors, Mucosal Immune Responses, and Contributions to Bacterial Vaginosis. Infect Immun. 2023;91(5):e0039022. doi:10.1128/iai.00390-22
Valenti P, Rosa L, Capobianco D, et al. Role of Lactobacilli and Lactoferrin in the Mucosal Cervicovaginal Defense. Front Immunol. 2018;9:376. doi:10.3389/fimmu.2018.00376
Vodstrcil LA, Plummer EL, Fairley CK, et al. Male-Partner Treatment to Prevent Recurrence of Bacterial Vaginosis. New England Journal of Medicine. 2025;392(10):947-957. doi:10.1056/NEJMoa2405404
