Background: In the United States, rates of sexually transmitted infections (STIs) have risen steadily in recent years as has PrEP use to prevent HIV infection. Our goal was to understand longitudinal patterns in the association between PrEP user and STIs. These analyses are a key target in prevention efforts aimed at disrupting the downstream HIV infection risk.
Methods: Data were collected as part of RADAR, a cohort study of young men who have sex with men (YMSM) and transgender women (TGW; aged 16-29) living in Chicago. Unadjusted and adjusted longitudinal lagged regression models were utilized to assess the relationship between PrEP use and odds of rectal STI acquisition. Analyses included data from six study visits. Mediation models were also utilized to consider the potential pathway between PrEP use, condomless sex, and STI diagnosis.
Results: Two hundred and eight-two (24.1%) participants reported PrEP use at least once across all study visits while 374 (31.9%) participants had a positive rectal STI test at least once. In longitudinal models, no significant association was observed between PrEP use and STI diagnosis (aOR=1.07, 95% CI: 0.63-1.82). This same finding was observed when comparing PrEP users to non-users as well as when comparing consistent PrEP users to those who varied their used between study visits. In mediation models, PrEP use was significantly associated with increased likelihood of condomless anal sex at the next study visit (CAS; aOR=1.61, 95% CI: 1.10-2.36), however, CAS was not associated with STI status (aOR=0.95, 95% CI: 0.58-1.57). Nor was there a significant difference in relationship between PrEP and STIs when stratifying either of these analyses by race/ethnicity.
Conclusions: We demonstrated that, overall, PrEP use was not associated with STIs among YMSM but did observe that PrEP users were more likely report increased participation in CAS at the subsequent study visit. In the talk, theories will be explored as to why an association exists between PrEP use and CAS but not between CAS and STIs.