HIV Pre-exposure Prophylaxis use and subsequent bacterial Sexually Transmitted Infections among gay, bisexual and other men who have sex with men


BACKGROUND: PrEP-using GBM may be more likely to engage in sexual behaviors associated with bacterial STI transmission. We assessed the associations between PrEP use, condomless anal sex (CAS), number of sex partners (NSP), oral sex (OS), and odds of acquiring a subsequent bacterial STI among GBM living in Canada.
METHODS: Among HIV-negative/unknown-status GBM from the baseline visit of the Engage Cohort Study, we fit a structural mediation model to estimate pathways between PrEP use at baseline, and sexual behaviors and bacterial STI diagnoses (gonorrhea, chlamydia and syphilis) at the 1-year follow-up visit.
RESULTS: Among 2,008 HIV-negative GBM at baseline, recruited from 2/2017 to 8/2019,341 (17.0%) used PrEP within the last 6 months and 136 (6.8%) were diagnosed with an STI at their 1-year follow-up visit.In the mediated model, the direct association between PrEP use at baseline and STIs at 1-year follow-up was non-significant; however, PrEP use was significantly associated with increased number of sex partners (β=.25; 95%CI,.18-.33;p<.001)andCAS (β=.18; 95%CI,.09-.28;p<.001), but not with oral sex (β=.02; 95%CI,-.10-.16;p=.76) at one-year follow-up. Two indirect paths were statistically significant: 1) PrEP'CAS'STI (β=.09; 95%CI,.03-.17: p=.02) and 2) PrEP'NSP'CAS'STI (β=.08; 95%CI,.03-.13: p=.001).
CONCLUSIONS: In mediation models, PrEP use at baseline was indirectly associated with future bacterial STIs among GBM. Findings suggest that PrEP use may lead to bacterial STIs via both an increased number of sex partners and increased engagement in CAS. Behavioural and biomedical interventions, including increased screening as per PrEP care and potential bacterial STI prophylaxis and vaccines, are needed to reduce PrEP-using GBM's risk of bacterial STIs.

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