Next generation sequencing to examine associations between vaginal washing and vaginal microbiota: A cohort study.

Background: The association between vaginal washing and HIV risk may be mediated by vaginal washing-associated changes in vaginal microbiota.
Methods: Data from a cohort of HIV-negative US and Kenyan women enrolled in the Preventing Vaginal Infections trial were analyzed. Vaginal fluid samples and vaginal washing data were collected every 2 months for 12 months. Bacterial relative abundances were measured by broad-range 16S rRNA gene polymerase chain reaction with next generation sequencing. Generalized estimating equations were used to evaluate the association between vaginal washing and i) the Shannon Diversity Index (SDI); and ii) mean change in percent bacterial relative abundances, with application of a 10% false discovery rate (FDR).
Results: Participants ( N = 111) contributed 93/630 (14.8%) vaginal washing visits. Mean SDI was 0.74 points higher (95% CI 0.35, 1.14; p < 0.001) at washing visits among US participants ( N = 26). Vaginal washing was not associated with SDI in Kenyan participants ( N = 85). There were no associations between vaginal washing and vaginal bacterial relative abundances after applying the FDR.
Conclusions: The discordant results in Kenyan versus US women suggests the link between vaginal washing and sub-optimal vaginal microbiota may be context specific. Vaginal microbial shifts may not fully explain the association between vaginal washing and HIV acquisition.