Bacterial vaginosis, race, and sexually transmitted infections: does race modify the association?

BACKGROUND: There are significant racial disparities in the prevalence of sexually transmitted infections (STIs) in the United States. The purpose of this study was to evaluate whether the association of bacterial vaginosis and incident STI is modified by race even after adjustment for sexual practices and other potential confounding variables.
METHODS: We evaluated the association of bacterial vaginosis (BV) and STI acquisition in a group of 523 women at high risk for unplanned pregnancies and STI. BV was diagnosed by both Gram stain and Amsel criteria. STIs included Chlamydia trachomatis, Neisseria gonorrhoeae, pelvic inflammatory disease, trichomoniasis, syphilis, and HIV. Cox regression estimated the associations and the synergy index assessed whether race modified the association of BV and incident STI.
RESULTS: Sixteen percent of participants developed an STI during the 2-year follow-up. Compared with white women without BV at baseline, the adjusted hazard ratios were as follows: white women with BV = 0.59; African American women without BV = 1.96; and African American women with BV = 2.86. The synergy index of 3.38 implies a combined association of BV and African American race with STI in excess of each factor individually.
CONCLUSIONS: African American race modifies the association of BV and incident STI. Future research should strive to determine the relative contributions of other factors, such as biologic variation, social network or the consequences of socioeconomic position, in this disparity.