Association of Bacterial Vaginosis With Chlamydia trachomatis Infection Among Women in Mombasa, Kenya: A Nested Case-Control Study

Objective: Evidence is mixed regarding the relationship between bacterial vaginosis (BV) and Chlamydia trachomatis (CT) acquisition; therefore, we assessed the relationship between recent BV and subsequent CT infection. Study Design: A nested case-control study was conducted using data and samples from cisgender women who reported engaging in transactional sex and who were participating in the Mombasa Cohort, a longitudinal study, in Kenya. BV was assessed monthly and categorized by Nugent score (0-6=Normal, 7-10=BV-positive); CT testing was conducted quarterly by nucleic acid amplification testing. For each CT case, 2 controls were randomly selected using incidence density sampling that tested negative for CT around the time a case tested positive for CT (index visit). Conditional logistic regression was used to estimate the odds of being a case between participants with and without BV at the prior visit (index-1). Results: Between September 2010 and November 2021, 89 cases and 178 controls were identified. The median interval between the index and index-1 visits was 61 days (interquartile range [IQR] 35-134) for cases and 33 days (IQR 28-42) for controls. At the index-1 visit, 42.7% of cases and 23.6% of controls had BV. The unadjusted odds of being a case were 2.50 times higher among participants with BV at the index-1 visit compared to those without BV (95% confidence interval (CI): 1.44, 4.33). After adjustment for age, years of sex work, and contraception, there remained two-fold higher odds of CT among those with BV (adjusted OR=2.03; 95% CI 1.07, 3.88). Conclusion: In this population of individuals at increased risk for CT exposure, recent BV was associated with subsequent CT infection. Further research is needed to assess how BV-associated bacteria and communities may enhance susceptibility to CT infection.