The role of sexual networks in studies of how BV and STIs increase the risk of subsequent reinfection

Abstract

Prior studies have demonstrated that both bacterial vaginosis (BV) and sexually transmitted infections (STIs) are strong independent risk factors for subsequent STI. In observational studies of this biological enhancement (BE) hypothesis, it is important to adjust for the risk of STI exposure so that the independent effect of BE can be assessed. We sought to model if two markers of local sexual network (partner concurrency and cumulative number of STIs) represented residual confounding in the models of risk for subsequent infection in a study that screened 3620 women for STIs every 3 months for a year. Mixed-effects logistic regression was used to calculate the odds ratios for an incident diagnosis of Chlamydia trachomatis, Neisseria gonorrhoeae, Trichomonas vaginalis and BV following a diagnosis of any of these four at the prior visit, controlling for the cumulative number of STIs and partner concurrency variables. We found that partner concurrency and cumulative number of STIs were each associated with incident infection, and in general, controlling for these variables reduced the strength of the association between prior and incident infections. We conclude that the frequently found association between prior and incident STIs is associated with both BE and sexual network structure.

Keywords: Bacterial vaginosis; Trichomonas vaginalis; chlamydia; gonorrhoea; partner concurrency; residual confounding; sexual network.

Fig. 1.

Comparison of high-risk (left) and low-risk (right) local sexual networks for individual B for acquisition of STIs. Individual D has STI A (yellow). The edge-width (width of the bar between individuals) is proportional to the risk of transmission of STIs between serodiscordant individuals (as defined by condom use, presence of BV, HSV-2, etc.). B's risk for acquisition of STI A is greater in the high- than the low-risk network despite no difference in her reported risk profile (excluding partner concurrency if this is asked for).

Fig. 2.

Illustration of various possible sequences of STI diagnoses by visit number for study participants. See text for details.