Background: Bacterial vaginosis (BV) is a common condition that can cause pregnancy complications and increase the transmission of sexually transmitted infections. BV is characterised by a shift from a low diversity, Lactobacillus-dominated vaginal microbial community to one dominated by a consortium of anaerobic bacteria including Gardnerella vaginalis. The role of individual taxa in disease causation is unknown. We investigated microbial and epidemiological factors associated with the development of incident-BV in nested case-control study within a two-year, prospective-cohort study of 298 women-who-have-sex-with-women.
Methods: Cases who developed BV (n=51) were matched with controls. Microbiota analysis was performed on 3-monthly vaginal specimens using 16S rRNA amplicon sequencing. Multivariable Cox regression analysis was used to investigate associations.
Findings: After adjustment for sexual behaviours and bacterial taxa present, reduced abundance of Lactobacillus crispatus (adjusted hazard ratio (AHR)=0.99,95%CI:0.97-1.00,p<0.038), increased abundance of Gardnerella vaginalis (AHR=1.02,95%CI:1.01-1.03,p<0.001), and detection of an uncultured BV-related bacterium (BVAB candidate division TM7; AHR=6.06,95%CI:1.99-18.43,p=0.002) were associated with incident BV. Compositional change in the vaginal microbiota was related to exposure to a new sex partner, and to having a particular microbiota composition.
Conclusions: This study confirmed the role of two key protagonists implicated in BV pathogenesis, L. crispatus and G. vaginalis, and found that exposure to new sexual partners drives key changes in vaginal microbiota associated with BV.