Previous studies have suggested that disruptions of the vaginal microbiota may increase women’s susceptibility to HIV infection. The authors were interested in the association between the concentrations of specific vaginal bacteria and increased risk of HIV acquisition in African women. They performed a nested case-control study of participants from eastern and southern Africa. Five cohorts of African women (female sex workers, pregnant and post-partum women, and women in serodiscordant relationships) were examined using sequence analysis of broad-range 16S rRNA gene PCR products (55 cases and 55 controls). 20 taxa were then selected for bacterium-specific real-time PCR assays on the full cohort as a four-category exposure (undetectable, first tertile, second tertile and third tertile of concentrations). The authors identified 87 women who acquired HIV infection (cases) and 262 controls who did not. They found that the vaginal bacterial community diversity was significantly higher in women who acquired HIV infection (median 1·3) than in seronegative controls (median 0·7). Seven of the 20 taxa demonstrated significant concentration-dependent associations with increased odds of HIV acquisition (significant results only): Parvimonas species type 1 (second tertile adjusted odds ratio [aOR] 3·01, 95%CI 1·13-7·99; third tertile aOR 4·64, 95%CI 1·73-12·46) and type 2 (first tertile aOR 3·52, 95%CI 1·63-7·61; third tertile aOR 2·18, 95%CI 1·01-4·72), Gemella asaccharolytica (first tertile aOR 2·09, 95%CI 1·01-4·36; third tertile aOR 3·03, 95%CI 1·46-6·30), Mycoplasma hominis (third tertile aOR 2·76, 95%CI 1·36-5·63), Leptotrichia/Sneathia (first tertile aOR 2·04, 95%CI 1·02-4·10; third tertile aOR 2·59, 95%CI 1·26-5·34), Eggerthella species type 1 (second tertile aOR 2·62, 95%CI 1·31-5·22), and vaginal Megasphaera species (first tertile aOR 3·15, 95%CI 1·45-6·81). Therefore differences in the vaginal microbial diversity and concentrations of key bacteria are associated with greater risk of HIV acquisition in women.
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