Infectious disease
Does bacterial vaginosis make HIV easier to pass to men?
Open access · cc by · source: Europe PMC
Men whose HIV-positive female partners had bacterial vaginosis were about three times more likely to catch HIV from them than men whose partners had normal vaginal bacteria.
Study at a glance
- Design
- Cohort — Secondary analysis of a prospective cohort nested in the Partners in Prevention HSV/HIV Transmission trial; vaginal flora graded by Gram stain every 3 months, with Cox models for time to genetically linked male HIV-1 infection.
- N
- N=2236 · 2,236 couples in which the woman had HIV-1; 50 genetically linked male infections with vaginal flora data were analysed as events.
- Population
- HIV-1 serodiscordant heterosexual couples in southern and East Africa where the female partner was HIV-positive (and HSV-2 positive, CD4 at least 250, not on ART) and the male partner HIV-negative.
- Outcome
- Female-to-male HIV-1 transmission confirmed as genetically linked by viral sequencing; secondary outcomes were genital and plasma HIV-1 RNA levels.
Structured fields used in claim comparison tables when every cited study has a complete layer.
Key findings
There were 57 genetically linked transmissions, of which 50 had vaginal flora results available. Transmission incidence was 2.91 per 100 person-years when the woman had bacterial vaginosis, versus 0.76 with normal flora, and after adjustment bacterial vaginosis carried a 3.17-fold higher risk. Intermediate flora was not linked to higher risk, and sensitivity analyses using different timing of the swab gave similar results. Bacterial vaginosis was associated with only a small rise (about 0.2 log) in genital HIV levels, which does not seem to fully explain the higher risk.
Methodology
The researchers followed 2,236 African couples in which the woman had HIV and the man did not, for up to two years, as part of a trial of herpes-suppressing therapy. Every three months the women's vaginal swabs were graded by Gram stain as normal flora, intermediate flora or bacterial vaginosis, and men were tested for HIV. New infections in men were counted only if viral sequencing showed the virus came from their partner, and the analysis adjusted for sexual behaviour, circumcision, other sexually transmitted infections, pregnancy and the woman's blood viral load.
Limitations
Vaginal flora was checked only every three months, but it can change weekly, so the flora at the moment of infection is unknown. The number of transmission events was small, making the estimate imprecise, and unmeasured confounding cannot be excluded in an observational analysis. Participants were a selected group (couples tested and counselled together, enrolled in a trial, women with relatively healthy immune systems and HSV-2 infection), so results may not generalise. The study does not show that treating bacterial vaginosis would reduce transmission; that requires a trial.
How this study connects
Role on claims
Each row is a claim on a concept or method page where this paper supports, challenges, or qualifies the statement. Roles are hand-checked — not a model guess.
Treating genital dysbiosis is a plausible, not proven, prevention target.
A co-infection in one partner can raise HIV transmission: in a prospective cohort of 2,236 serodiscordant African couples, bacterial vaginosis in the HIV-positive woman carried a 3.17-fold adjusted risk of genetically linked transmission to the male partner, only partly explained by a small (~0.2 log) rise in genital HIV RNA.
Evidence for the claim as stated.
The bacterial vaginosis result is from women with HSV-2, CD4 ≥250 and not on ART, with only 50 analysable transmissions; it may not apply where partners are virally suppressed.
Evidence for the claim as stated.
Open questions
Tensions this paper is part of
From concept pages' “where studies disagree.” Disagreement means the same question; scope means different assays, populations, or outcomes.
The bacterial vaginosis result is from women with HSV-2, CD4 ≥250 and not on ART, with only 50 analysable transmissions; it may not apply where partners are virally suppressed.
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