Background Bacterial vaginosis (BV) is a highly prevalent infection that frequently recurs following standard treatment. In a randomised controlled trial (RCT) of oral periodic presumptive treatment (PPT) to reduce vaginal infections among Kenyan women, we observed a decrease in BV and an increase in Lactobacillus colonisation among women randomised to receive 2 g metronidazole +150 mg fluconazole monthly for 12 months. After the trial, women were invited to continue follow-up in an open cohort study. These post-trial data were analysed to test the hypothesis that the treatment effect would persist in the absence of PPT.

Methods Data were obtained from women who completed all 12 RCT visits and attended ≥1 cohort study visit within 120 days of their final RCT visit. We used Andersen-Gill proportional hazards models to estimate the post-trial effect of the intervention vs placebo on the incidence of BV by Gram stain (Nugent score ≥7) and Lactobacillus species by culture on Rogosa agar.

Results The RCT enrolled 310 subjects (155 per arm), of whom 165 (83 active and 82 placebo) were included in this analysis. Included subjects were slightly older (median (IQR): 33 years (29–39) vs 30 years (26–35); p<0.001) and reported a longer duration of sex work (median (IQR): 6 years (2–11) vs 3 years (1–6); p<0.001) compared to those excluded. At the final RCT visit, which represented the baseline visit for this analysis, demographic and behavioural characteristics were similar by arm. The prevalence of BV at the final RCT visit was 16% in the active arm and 43% in the placebo arm (p<0.001). The post-trial incidence of BV was 260/100 person-years (p-yrs) in the active arm vs 358/100 p-yrs in the placebo arm (HR=0.76; 95% CI: 0.51% to 1.12%). The prevalence of Lactobacillus colonisation at the final RCT visit was 17% in the active arm and 18% in the placebo arm (p=0.81). The post-trial incidence of Lactobacillus colonisation was 180/100 p-yrs in the active arm vs 127/100 p-yrs in the placebo arm (HR=1.42; 95% CI: 0.85% to 2.71%).

Conclusions Despite a decrease in BV and an increase in Lactobacillus colonisation during the RCT, the effect of PPT was not sustained during the 120 days following cessation of the intervention. New interventions that reduce BV recurrence and promote long-term Lactobacillus colonisation without the need for ongoing PPT or suppressive therapy are needed.