High Concentrations of Key Vaginal Bacteria May Increase Risk for HIV Acquisition

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Vaginal bacterial community diversity was higher in women who acquired HIV infection than in seronegative women.
Vaginal bacterial community diversity was higher in women who acquired HIV infection than in seronegative women.

Concentrations of specific vaginal bacteria were associated with a greater risk for HIV acquisition in women, according to recent research published in the Lancet Infectious Diseases.

In this case-control study spanning 6 sub-Saharan African countries, 5 cohorts of HIV seronegative women provided vaginal samples for microbiota analyses and were followed-up every 1 to 3 months for additional samples and HIV testing from 2004 to 2014. Patients were evaluated for concentrations of specific vaginal bacteria associated with increased risk for HIV acquisition. The 5 cohorts of women included 3 risk groups: sex workers, pregnant and postpartum women, and HIV-negative women in serodiscordant relationships.

During the 10-year time span, 262 control participants did not acquire HIV infection and 87 case participants did acquire HIV infection. Two bacterial PCR techniques were used to evaluate the relative abundance of vaginal bacteria and the association with HIV acquisition.

To compare the overall vaginal bacterial community diversity, 55 cases and 55 control vaginal samples were evaluated via pyrosequencing. The Shannon Diversity Index was significantly higher in cases than controls. Furthermore, comparing the relative abundance of vaginal bacteria, 20 different taxa showed a significant trend toward an association with HIV acquisition.

To identify individual bacterium-specific associations with HIV acquisition, the 20 key taxa were selected for taxon-directed real-time PCR testing. After adjustment for potential cofounders, 7 taxa showed significant associations with HIV acquisition and 4 of these taxa showed associations that were strongest at the highest concentrations.

In addition, a validation analysis was performed in a subset of samples not included in the pyrosequencing step. This analysis confirmed 5 of the 7 bacteria identified in the primary analysis to show an association with HIV acquisition, including Mycoplasma hominis (adjusted odds ratio [aOR], 2.71; P =.026), Eggerthella species type 1 (aOR, 2.50; P =.035), Leptotrichia/Sneathia (aOR, 2.47; P =.056), Gemella asaccharolytica (aOR, 2.45; P =.040), and Parvimonas species type 2 (aOR, 2.43; P =.042). The 2 bacteria excluded from the 7 identified in the primary analysis were Parvimonas species type 1 and Megasphaera.

Several sensitivity analyses were applied to the 7 bacterial taxa associated with HIV acquisition from the primary analysis. These associations were consistent across all 3 risk groups regardless of risk factors, demographics, or incidence observed in the cohorts.

The study authors concluded that their results contributed to "defining individual vaginal bacteria that are associated with HIV risk in women [and] could provide additional specific targets and inform future strategies for HIV prevention research."

Reference

McClelland RS, Lingappa JR, Srinivasan S, et al. Evaluation of the association between the concentrations of key vaginal bacteria and the increased risk of HIV acquisition in African women from five cohorts: a nested case-control study [published online January 25, 2018]. Lancet Infect Dis. doi: 10.1016/S1473-3099(18)30058-6

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