Bacterial Vaginosis: Why Current Treatments Fail and What the Future Holds

Table of Contents

• Key Points
• Understanding Bacterial Vaginosis
• The Global Burden of BV
• Current Treatments and Their Limitations
• Why Does BV Keep Coming Back?
• Evidence for Sexual Transmission of BV
• Male Partner Treatment Trials: A Complicated History
• Biofilm: A Hidden Barrier to Cure
• Innovative Biofilm-Disrupting Strategies
• Antimicrobial Resistance: A Growing Concern
• Clinical Implications for Patients
• Study Limitations and Open Questions
• Recommendations for Patients and Researchers
• Frequently Asked Questions
• Source Information

Key Points

• BV recurs in over half of treated women within 6–12 months despite successful initial therapy.
• Recurrence is linked to persistent bacterial biofilm, possible reinfection from partners, and subtle antimicrobial resistance.
• Standard treatments include 7-day oral metronidazole, 7-day clindamycin cream, or 5-day metronidazole gel; short courses are less effective.
• Evidence suggests sexual transmission plays a role, but male partner treatment trials have been inconclusive due to design flaws.
• Future strategies may combine antibiotics with biofilm-disrupting agents and partner treatment, though these are not yet ready for clinical use.

Understanding Bacterial Vaginosis

Bacterial vaginosis (BV) is not simply an infection in the traditional sense — it represents a profound shift in the vaginal microbiome (the community of microorganisms that naturally live in the vagina). In a healthy vagina, key protective bacteria called Lactobacillus species — particularly Lactobacillus crispatus — dominate the environment. These beneficial bacteria produce lactic acid, bacteriocins, and other antimicrobial molecules that help defend against harmful pathogens.

In women with BV, this protective community is dramatically depleted. In its place, a highly diverse population of bacteria takes over, including Gardnerella vaginalis, Atopobium vaginae, and other fastidious (difficult-to-culture) bacteria such as Megasphaera, Sneathia, and Clostridiales species. This shift is accompanied by increased production of volatile amines (chemicals that cause the characteristic fishy odor) and a rise in vaginal pH above 4.5.

Recent studies have identified a key player in BV's persistence: a polymicrobial biofilm — a thin, sticky, protective layer of bacteria adherent to vaginal epithelial cells — dominated by G. vaginalis and A. vaginae. This biofilm is present in women with BV and appears to be absent in healthy controls. The initiating event that triggers this adverse shift remains unclear, and this lack of understanding has been a major obstacle to developing better treatments.

The Global Burden of BV

BV carries a high global burden among women of reproductive age. Prevalence estimates vary significantly by region:

• 12% in Australian women
• 29% in North American women li>
• Over 50% in women in East and Southern Africa

More than 50% of women with BV experience an unpleasant vaginal malodor and discharge. Qualitative studies have shown that BV is associated with a significant negative impact on self-esteem, sexual relationships, and overall quality of life.

The consequences extend far beyond discomfort. BV is associated with an approximately 2-fold increased risk of acquiring a broad range of sexually transmitted infections (STIs), including chlamydial infection, gonorrhea, herpes simplex type 2, and human immunodeficiency virus (HIV). Women with HIV who have BV also face an increased risk of transmitting HIV to male partners.

BV is also linked to serious reproductive and obstetric complications. Women with BV have an elevated risk of pelvic inflammatory disease, spontaneous abortion, preterm delivery, low birth weight, and postpartum endometritis (inflammation of the uterine lining after childbirth). These potential consequences make effective, lasting treatment a critical public health priority.

Current Treatments and Their Limitations

Current clinical approaches to managing BV are somewhat empirical, relying on two classes of antimicrobials with broad-spectrum anaerobic coverage: nitroimidazoles and clindamycin. The recommended first-line regimens are:

• Oral metronidazole 500 mg twice daily for 7 days
• Intravaginal 2% clindamycin cream once daily for 7 days
• Intravaginal metronidazole gel once daily for 5 days

Importantly, single doses and short courses of metronidazole, tinidazole, and intravaginal clindamycin are less effective and are not recommended as first-line therapy.

Short-term cure rates following these first-line regimens are equivalent to each other and approach 80%. However, studies with extended follow-up reveal a sobering reality: recurrence rates exceed 50% within 6 to 12 months. This means that even when treatment initially succeeds, more than half of women will experience a return of BV within a year.

These high recurrence rates have led investigators to evaluate a range of alternative therapeutic approaches, including extended and suppressive antimicrobial regimens, combination first-line regimens, and adjunctive intravaginal and oral probiotic therapies. While some of these approaches appear promising and are under further evaluation, overall there has been limited progress in achieving sustained long-term cure after stopping treatment.

Why Does BV Keep Coming Back?

The lack of therapeutic success reflects a poor understanding of the pathogenesis (disease mechanism) of both recurrent and newly acquired BV. Researchers are investigating three main contributors to recurrence:

1. Persistence of BV-associated bacteria: One study found that higher baseline loads of some BV-associated bacteria were associated with an increased risk of recurrence.
2. Biofilm re-accumulation: Two studies showed that BV-associated biofilm re-accumulates following antibiotic therapy, indicating that persistence of certain bacteria and their protective biofilm may be a key determinant of recurrence.
3. Antimicrobial resistance: There is some evidence that clindamycin use can result in the emergence of clindamycin-resistant anaerobic gram-negative rods. However, in a panel of 865 anaerobic species obtained from women with BV, resistance to metronidazole was rare — only 0.3%.

One intriguing finding comes from recent whole-metagenome sequencing studies, which have identified at least 4 distinct clades (subgroups) of G. vaginalis. Preliminary studies suggest that 2 of these clades may be intrinsically resistant to metronidazole, providing one possible mechanism for BV persistence after treatment.

There are also tantalizing data suggesting that reintroduction of BV-associated bacteria through sexual intercourse may contribute to BV recurrence, raising the question of whether sexual transmission or exchange of bacteria between partners plays an integral role in BV pathogenesis and recurrence.

Evidence for Sexual Transmission of BV

The proposition that BV may be sexually transmitted has appeared in published literature for several decades. However, confusion regarding the cause of BV, difficulty in identifying a single causative agent, and the absence of a clear disease counterpart in males have all complicated efforts to determine whether BV is truly sexually transmitted.

The historical evidence dates back to the 1950s, when a highly unethical study demonstrated that women inoculated with secretions from women with BV — but not with a pure culture of G. vaginalis alone — developed BV. This led to the belief that BV was likely sexually transmitted.

A mounting body of epidemiologic and microbiologic data now suggests that sexual transmission is indeed integral to BV pathogenesis. Key supportive evidence includes:

• A meta-analysis found that BV detection is associated with inconsistent condom use and exposure to increased numbers of recent and lifetime sexual partners.
• Women with BV have an earlier median age of sexual debut than women without BV.
• While 2 studies identified BV in "virgins," both restricted the definition of "virgin" to absence of a past history of penile-vaginal sex.
• In contrast, a study of young female students that collected detailed data on sexual behaviors found that BV was not detected in women without a history of sexual activity with others. BV was uncommon in women who reported only noncoital sexual activities, and was significantly associated with the practice of penile-vaginal sex.

Consistent epidemiological data also show high rates of BV concordance within female partnerships. BV has been associated with practices that implicate sexual transmission between women, including increased number of female partners, having a female partner with BV, and receptive oral sex.

Additional evidence comes from a study by Marrazzo and colleagues, who showed that women who have sex with women in monogamous relationships share Lactobacillus strain types. A 2-year cohort study by Vodstrcil and colleagues found that incident BV was associated with exposure to a new female sexual partner and a female partner with BV symptoms. These data suggest that dynamic exchange of both protective and detrimental vaginal bacterial species occurs between women in sexual relationships.

Published data also support the idea that reintroduction of BV-associated bacteria through sexual intercourse likely contributes to BV recurrence after treatment. In 2 studies, treated women with ongoing exposure to an untreated male partner had twice the risk of recurrence, even after adjusting for sex frequency, condom use, and contraception. Several studies have found that inconsistent condom use during penile-vaginal sex increased the risk of recurrence following treatment.

Even more direct evidence comes from deep-sequencing studies showing that the subpreputial space (the area under the foreskin) and distal urethra of males can harbor a broad range of BV-associated bacteria. These bacteria are more prevalent among the male partners of females with BV than among those of females without BV. The composition of this sulcus microbiota appears to be strongly influenced by circumcision and sexual activity.

Male circumcision has been prospectively associated with a significant reduction in BV-associated genera and a 40%–60% reduction in the development of BV in female partners. BV-associated biofilm has recently been detected in male urine and semen and is more commonly found in the male partners of females with BV than in healthy controls.

Male Partner Treatment Trials: A Complicated History

Following the 1950s discovery, 6 randomized, controlled male-partner-treatment trials were conducted from the mid-1980s to the 1990s. The results were mixed and confusing:

• 3 trials found male partner treatment associated with a reduction in either BV recurrence or BV symptoms in women, although this was statistically significant in only 1 trial (Mengel and colleagues). The Mengel trial reported a significant increase in symptom resolution and BV cure by Gram stain in women whose partners received either a 7-day course or a 2-g dose of metronidazole.
• Vutyanavic and colleagues reported a 13% increase in clinical cure of BV among women at 4 weeks whose male partners had been treated with 2 g of tinidazole.
• Vejtorp and colleagues found a 15% reduction in BV and a 36% reduction in culture of G. vaginalis at 5 weeks in women whose male partners were treated with two 2-g doses of metronidazole; neither finding was statistically significant.
• 2 trials found no effect on BV recurrence from treating male partners with a single dose or 7-day course of metronidazole, or with oral clindamycin for 1 week.
• 1 trial paradoxically found BV recurrence to be higher among women whose partners were treated with two 2-g doses of metronidazole, compared with those who were not treated.

The apparent contradiction between the strong evidence for sexual transmission and the failure of these trials now appears likely due to issues in trial design, as detailed in a rigorous systematic review by Mehta. Mehta found that:

• None of the trials had sufficient statistical power to detect reasonable effect sizes
• Randomization methods were deficient or insufficiently reported
• Adherence to therapy was not reported in women and was only reported in men in 2 trials
• 5 trials used treatment regimens in women that are now considered less effective (such as single-dose regimens)
• 5 trials used regimens in men that are now known to be suboptimal in women

Mehta concluded that the trial findings were inconclusive by current clinical trial standards and recommended that sufficiently powered trials using recommended therapies be conducted to determine whether antibiotic treatment in men can reduce BV recurrence in their female partners.

There is currently 1 registered male-partner-treatment trial enrolling couples in North America, in which men are randomly assigned to receive a 7-day course of oral metronidazole versus oral placebo (ClinicalTrials.gov identifier NCT02209519). Results are eagerly awaited. Trials involving topical antimicrobials in addition to oral agents are also planned, as these may be required to eradicate cutaneous (skin-surface) carriage of BV-associated bacteria on the penile skin. Female-partner-treatment trials are also clearly needed, though their design will require innovative thinking due to logistical challenges.

Biofilm: A Hidden Barrier to Cure

There is compelling evidence for the existence of pathogen-containing biofilm in the vagina of women with BV and on the urethra and subpreputial surface of the glans penis of males. This biofilm provides a rational explanation for microbial persistence after therapy. Biofilm has been shown to persist after putatively successful antimicrobial therapy in females.

Biofilm may serve to reduce antimicrobial penetration, allowing antibiotic-susceptible microbes to survive in a protected "carrier state." This sanctuary function of biofilm may well explain the failure of what appears, in the laboratory, to be highly effective antimicrobial therapy. Understanding biofilm production also provides insight into the expression of bacterial virulence factors (the mechanisms bacteria use to cause disease). It may be necessary to break down biofilm to achieve optimal efficacy of antimicrobial therapies, and novel strategies to eliminate biofilm have emerged targeting women with recurrent BV.

Innovative Biofilm-Disrupting Strategies

The first evidence of a potential therapeutic benefit from biofilm disruption emerged in a multicenter, long-term study of maintenance suppressive therapy for recurrent BV. In this study by Reichman and colleagues, women received topical boric acid 600 mg daily following a 1-week course of systemic nitroimidazole therapy. After a 1-month course of daily boric acid treatment, asymptomatic women were additionally prescribed suppressive twice-weekly metronidazole for 4 months. The overall combination regimen dramatically reduced BV recurrence during treatment, although recurrence after treatment stopped was common.

Importantly, previous unpublished studies by Sobel and colleagues had demonstrated that boric acid alone was inadequate in even achieving a satisfactory clinical response in BV, reflecting its weak antimicrobial potency. Unfortunately, the study design precluded objective evaluation of the unique contribution of boric acid. Ongoing research is also evaluating boric acid enhanced with an ethylenediaminetetraacetic acid (EDTA) excipient, which boosts antimicrobial activity and retains activity against vaginal biofilm.

These clinical studies, together with the biofilm research by Swidsinski and colleagues, have heightened interest in identifying more-potent biofilm-disrupting agents. Candidates under investigation include:

• Octenidine: An antiseptic with broad-spectrum antimicrobial activity, effective against biofilms involved in oral, wound, and orthopedic-implant infections. Swidsinski reported on its use in 24 women with recurrent BV. With daily application for 7 days, and in women with further recurrence, daily for 28 days and weekly for 60 days, initial cure rates looked promising. However, the efficacy of prolonged and repeated treatment was poor, and BV recurrence was observed in a significant proportion of women.
• DNases: G. vaginalis biofilms contain extracellular DNA (eDNA), which is integral to their structural integrity. Enzymatic disruption of this eDNA by DNase has been shown to inhibit G. vaginalis biofilm formation and to disrupt established biofilms in the laboratory. Hymes and colleagues reported that low concentrations of DNase and metronidazole together were more efficacious against G. vaginalis biofilm than either agent alone, possibly due to increased susceptibility of G. vaginalis to the antibiotic when liberated from the biofilm.
• Retrocyclin (RC-101): A synthetic antimicrobial peptide with antiviral activity that has been shown to inhibit the formation of G. vaginalis biofilms in vitro. RC-101 is a potent inhibitor of vaginolysin, a toxin produced by G. vaginalis. Vaginolisin inhibition has been proposed as a potential strategy for BV treatment.
• Quorum-sensing inhibitors: Quorum sensing is a strategy some bacterial species use to coordinate expression of genes involved in virulence, biofilm formation, and pathogenicity. While quorum-sensing inhibitors have not yet been evaluated in human studies, they have been shown to be active in vitro against biofilms produced by Pseudomonas aeruginosa and Staphylococcus species.
• Naturally occurring antimicrobials: Including subtilosin, poly-L-lysine, and lauramide arginine ethyl ester.

Of all these agents, only octenidine and boric acid have been evaluated in human studies. BV research lags behind other fields — such as intravascular catheter and prosthetic device infection research — where biofilm prevention and removal have been studied extensively. One significant impediment has been the lack of a suitable animal model, as vaginal primate and other animal models are less than optimal due to significant differences in their microbiota and pH compared to humans. There is an urgent need for progress in developing and evaluating safe and effective topical vaginal agents capable of disrupting and eliminating genitourinary tract biofilm.

Antimicrobial Resistance: A Growing Concern

There remains scant knowledge regarding the role of antimicrobial resistance in contributing to both initial clinical and bacteriologic failures and recurrence. Clinical experience indicates that initial treatment failure is uncommon, whereas relapse after initial improvement is much more common.

Beigi and colleagues performed one of the few studies examining in vitro resistance to cultivatable BV-associated bacteria, concluding that, in contrast to clindamycin, anaerobic gram-negative bacterial resistance to metronidazole was rare (0.3% in a panel of 865 anaerobic species). Similar in vitro studies specifically focusing on women with refractory or recurrent BV have not been performed.

A major limitation of such studies is that the majority of BV-associated bacteria cannot be grown in the laboratory and thus cannot be tested for antimicrobial susceptibility. It should also be emphasized that BV represents a functional dysbiosis — a community disturbance involving multiple contributing pathogens — reflecting a model that is difficult, if not impossible, to evaluate in vitro using traditional antimicrobial susceptibility testing methods.

Both G. vaginalis and A. vaginae demonstrate well-described intrinsic resistance to nitroimidazole agents. Nevertheless, in living tissue (in vivo), these organisms are dramatically reduced in population numbers following conventional nitroimidazole therapy. This indicates an effective in situ effect, possibly reflecting the action of more-potent antimicrobial intermediate or degradation products.

It has always been assumed that currently recommended regimens of oral and topical nitroimidazoles achieve concentrations in vaginal secretions far above levels needed to eradicate BV pathogens. However, some investigators believe higher concentrations may be more effective and essential — especially given the possibility of microbial pathogen persistence in biofilm. The use of available topical formulations of metronidazole results in vaginal fluid drug concentrations that are 10–30-fold higher than achievable with the oral drug. Several uncontrolled, noncomparative pilot studies using higher-dose topical metronidazole have reported improved cure and control rates. The authors note there is a need for studies comparing high-dose topical metronidazole with conventional-dose, commercially available metronidazole — especially given the availability and documented safety of high-concentration preparations.

Clinical Implications for Patients

For women living with recurrent BV, this research carries several important messages. First, the frustrating pattern of treatment followed by recurrence is not a personal failure — it reflects fundamental biological processes, including biofilm persistence and possible reinfection from partners, that are only now being understood.

Second, current treatment guidelines should still be followed. The authors recommend adhering to established regimens — oral metronidazole 500 mg twice daily for 7 days, intravaginal 2% clindamycin cream once daily for 7 days, or intravaginal metronidazole gel once daily for 5 days — rather than relying on unproven alternative regimens. Short-course and single-dose treatments are less effective and should be avoided.

Third, patients should be aware that probiotics, although attractive as supplementary agents, have not consistently been shown to be advantageous in clinical studies.

Fourth, the evidence around sexual transmission suggests practical preventive steps. Consistent condom use during penile-vaginal sex appears to reduce the risk of recurrence. The data also suggest an unforeseen benefit from male circumcision in reducing BV in female partners — a 40%–60% reduction in some studies. For women who have sex with women, the concordance of BV within partnerships and the association with new female partners with BV symptoms suggest that partner treatment may be relevant in these relationships as well, though more research is needed.

Study Limitations and Open Questions

The authors acknowledge several important limitations in the current evidence base. A major unresolved issue is the incomplete understanding of the pathophysiology of BV, which has been a significant impediment to developing optimal treatment and prevention approaches.

New drugs have not been forthcoming and are not likely to be available in the immediate future. The historical partner-treatment trials were underpowered and had significant design flaws by modern standards, meaning conclusions about partner treatment effectiveness cannot be drawn from them. Biofilm research in BV lags behind other fields due to the lack of suitable animal models, and most agents with potential biofilm-disrupting activity have only been tested in the laboratory, not in humans.

Future research should also focus on the possibility that BV is a heterogeneous condition involving subtly different vaginal microbiomes. Such putative BV subtypes might respond differently to treatment regimens, and identifying these subtypes could allow more personalized treatment approaches.

Recommendations for Patients and Researchers

Based on this review, the authors offer the following recommendations:

1. Follow current guidelines: Patients should complete the full recommended course of first-line therapy — 7 days of oral metronidazole, 7 days of intravaginal clindamycin cream, or 5 days of intravaginal metronidazole gel — rather than unproven alternative regimens.
2. Consider condom use: Consistent condom use appears to reduce the risk of BV recurrence after treatment, likely by preventing reintroduction of BV-associated bacteria.
3. Support further research: Rigorous, sufficiently powered partner-treatment trials using recommended therapies are essential to determine whether antibiotic treatment in male partners can reduce BV recurrence in women. The results of the ongoing North American trial (NCT02209519) are eagerly awaited.
4. Watch for combination approaches: The future of BV treatment may lie in combination strategies — antibiotics given along with biofilm-disrupting agents and used in conjunction with partner treatment. While these approaches are not yet ready for clinical use, they represent the most promising path toward sustained cure.
5. Participate in clinical research: Women with recurrent BV may wish to consider enrolling in clinical trials, as current treatment options remain extremely limited and research progress depends on patient participation.

The authors conclude that despite the acknowledged limitations of current therapy, there is genuine hope for the future. Increasing recognition of the potential role of pathogen-rich biofilm in facilitating disease persistence — together with the future introduction of effective antibiofilm agents — results in real hope for improved therapeutic success. It is also important to acknowledge that reinfection from partners may be contributing to recurrence and may obscure the benefits of new therapeutic approaches.

Ultimately, optimal future BV treatment strategies may require combination approaches: antibiotics paired with biofilm-disrupting agents, and partner treatment for those at risk of reinfection. This comprehensive strategy offers the best hope for achieving sustained cure and reducing the serious sequelae associated with BV, including preterm delivery and increased susceptibility to sexually transmitted infections.

Frequently Asked Questions

Why does bacterial vaginosis keep coming back after successful treatment?

More than half of women treated for bacterial vaginosis experience recurrence within 6 to 12 months. Research suggests three key contributors: persistence of BV-associated bacteria, re-accumulation of a protective biofilm, and possible reinfection through sexual intercourse. Antimicrobial resistance may also play a role in some cases. These factors are still being studied.

Is bacterial vaginosis sexually transmitted?

Evidence strongly suggests sexual transmission contributes to BV, though no single cause has been proven. Studies show BV is associated with inconsistent condom use, new or multiple sexual partners, and higher rates in female partners of affected women. Male partners can carry BV-associated bacteria. However, trials treating male partners have had mixed results due to design flaws.

What are the recommended first-line treatments for bacterial vaginosis?

Current guidelines recommend one of three regimens: oral metronidazole 500 mg twice daily for 7 days, intravaginal 2% clindamycin cream once daily for 7 days, or intravaginal metronidazole gel once daily for 5 days. Short-course and single-dose treatments are less effective and should be avoided according to the authors.

Should my male partner be treated for bacterial vaginosis to prevent my recurrence?

Historically, six trials of male partner treatment gave mixed results, but they had major design flaws and were underpowered. A rigorous review concluded the issue remains unresolved. One new trial is currently enrolling couples to test a 7-day course of oral metronidazole in men. For now, routine partner treatment is not established.

What is a biofilm and how does it affect bacterial vaginosis treatment?

In BV, a thin, sticky protective layer of bacteria, called a biofilm, attaches to vaginal cells. This biofilm, dominated by Gardnerella and Atopobium, can persist after antibiotic therapy and may reduce antimicrobial penetration, allowing bacteria to survive. It appears to be a key reason BV often recurs, and new strategies aim to disrupt it.

Can probiotics help treat or prevent bacterial vaginosis?

Probiotics are attractive as a supplementary approach, but the authors note they have not consistently been shown to be advantageous in clinical studies. While some research on various probiotic regimens appears promising, overall evidence is limited. It is safest to follow recommended antibiotic treatments and discuss any additional therapies with your doctor.

What practical steps can reduce my risk of BV recurrence after treatment?

The authors recommend completing the full recommended course of first-line therapy, using consistent condoms during penile-vaginal sex, and avoiding unproven short-course regimens. Male circumcision was associated with a 40%–60% reduction in BV in female partners in some studies. Probiotics have not consistently been shown to help. Partner treatment remains unproven.

I have bacterial vaginosis that keeps coming back after antibiotics. Should I get a second opinion about my treatment plan?

Recurrent bacterial vaginosis after a full course of antibiotics is common: more than half of women have recurrence within 6 to 12 months. Current first-line therapy consists of 7 days of oral metronidazole, 7 days of intravaginal clindamycin cream, or 5 days of intravaginal metronidazole gel; shorter courses are less effective. A second opinion can help confirm that the treatment plan follows these guidelines and explore whether biofilm-disrupting or partner-treatment strategies under investigation might be relevant, though they are not yet standard. Diagnostic Detectives Network provides independent expert second opinions.

Source Information

Original Article: "Current Treatment of Bacterial Vaginosis Limitations and Need for Innovation"

Authors: Catriona S. Bradshaw, M.D., and Jack D. Sobel, M.D. (contributed equally to this work)

Affiliations: Melbourne Sexual Health Centre and Central Clinical School, Monash University, Clayton, Australia; Division of Infectious Diseases, Department of Internal Medicine, Wayne State University School of Medicine, Detroit, Michigan

Publication: The Journal of Infectious Diseases, 2016;214(S1):S14–20. Published by Oxford University Press for the Infectious Diseases Society of America. DOI: 10.1093/infdis/jiw159

Presented in part: Bacterial Vaginosis Technical Consultation Meeting of the Sexually Transmitted Infections Clinical Trials Group, Washington, D.C., April 8–9, 2015.

This patient-friendly article is based on peer-reviewed research.