McClelland RS, et al. - Researchers sought to evaluate the association between the concentrations of specific vaginal bacteria and increased risk of HIV acquisition in African women. They noted a greater risk of HIV acquisition among women in association with differences in the vaginal microbial diversity and concentrations of key bacteria. Defining vaginal bacterial taxa associated with HIV risk might help in determining mechanisms that influence HIV susceptibility and might provide important targets for future prevention research.

Methods

• A nested case-control study was conducted of participants from eastern and southern Africa.
• Researchers used data from five cohorts of African women (female sex workers, pregnant and post-partum women, and women in serodiscordant relationships) to form a nested case-control analysis between women who acquired HIV infection vs those who remained seronegative.
• They applied deep sequence analysis of broad-range 16S rRNA gene PCR products to a subset of 55 cases and 55 controls.
• From the data, they selected 20 taxa for bacterium-specific real-time PCR assays; these taxa were examined in the full cohort as a four-category exposure (undetectable, first tertile, second tertile, and third tertile of concentrations).
• They utilized conditional logistic regression to generate odds ratios (ORs) and 95% CIs.
• They stratified regression models by cohort, and generated adjusted ORs (aORs) from a multivariable model controlling for confounding variables.
• Bacterial diversity was measured using the Shannon Diversity Index.
• They primarily analyzed the associations between bacterial concentrations and risk of HIV acquisition.

Results

• Eighty seven women who acquired HIV infection (cases) and 262 controls who did not acquire HIV infection were identified between November, 2004, and August, 2014.
• Women who acquired HIV infection showed higher vaginal bacterial community diversity (median 1·3, IQR 0·4–2·3) than in seronegative controls (0·7, 0·1–1·5; p=0·03).
• In this study, 7 of the 20 taxa demonstrated significant concentration-dependent associations with increased odds of HIV acquisition: Parvimonas species type 1 (first tertile aOR 1·67, 95% CI 0·61–4·57; second tertile 3·01, 1·13–7·99; third tertile 4·64, 1·73–12·46; p=0·005) and type 2 (first tertile 3·52, 1·63–7·61; second tertile 0·85, 0·36–2·02; third tertile 2·18, 1·01–4·72; p=0·004), Gemella asaccharolytica (first tertile 2·09, 1·01–4·36; second tertile 2·02, 0·98–4·17; third tertile 3·03, 1·46–6·30; p=0·010), Mycoplasma hominis (first tertile 1·46, 0·69–3·11; second tertile 1·40, 0·66–2·98; third tertile 2·76, 1·36–5·63; p=0·048), Leptotrichia/Sneathia (first tertile 2·04, 1·02–4·10; second tertile 1·45, 0·70–3·00; third tertile 2·59, 1·26–5·34; p=0·046), Eggerthella species type 1 (first tertile 1·79, 0·88–3·64; second tertile 2·62, 1·31–5·22; third tertile 1·53, 0·72–3·28; p=0·041), and vaginal Megasphaera species (first tertile 3·15, 1·45–6·81; second tertile 1·43, 0·65–3·14; third tertile 1·32, 0·57–3·05; p=0·038).