(P6-LB) Factors associated with chemsex and sexually transmitted infection positivity in individuals attending self-screening clinics: A cross-sectional study in Québec, Canada

Chemsex, sexual engagement under drug influence, is associated with increased risks of sexually transmitted infections (STI). While chemsex has been primarily studied in at-risk populations, there is limited data in unselected populations. We aimed to assess prevalence and factors associated with chemsex, and compare STI positivity proportions between chemsex users and non-users attending STBBI self-screening clinics.

We performed cross-sectional analysis on unselected population attending Prélib self-screening clinics (Québec, Canada) from 12/2018 to 11/2022. We evaluated factors associated with chemsex with multivariable logistic regression with predictor variables: age range, self-identified gender, new sex partner, last unprotected sex ( < 2 months), sex worker, men who have sex with men (MSM), drug use (past year), past STI diagnosis, and pre-exposure prophylaxis (PrEP). We assessed difference in STI positivity proportions (including first valid tests) between chemsex and no-chemsex groups with Fisher’s exact test.

There were 41050 complete unique patient risk assessment questionnaires. Minority (n=958, 2.3%) reported chemsex in the past 6 months; the rest (n=40092, 97.7%) reported no chemsex. Factors associated with chemsex included age 50 years or older [aOR 1.8 (95% CI 1.2, 2.6)], self-identified gender of non-binary [1.6 (1.1, 2.4)], trans-female [4.8 (2.3, 9.5)], and other [3.6 (1.3, 8.5)], last unprotected sex ( < 2 months) [1.4 (1.2, 1.7)], sex worker [3.1 (2.3, 4.2)], MSM [3.3 (2.7, 4.0)], drug use (past year) [8.1 (7.0, 9.4)], past STI diagnosis [1.3 (1.1, 1.5)], taking PrEP everyday [3.6 (2.0, 6.6)] and sometimes [2.8 (1.5, 6.6)]. Higher proportion of chemsex users tested positive for any STI (13% v. 7%, p < 0.0001), NG anal (8% v. 3%, p < 0.0001) and oral (7% v. 1%, p < 0.0001), and HIV (0.4% v. 0.02%, p = 0.007).

In a large sample of unselected patients attending self-screening clinics, chemsex was associated with older age, self-identified gender, unprotected sex, sex worker, MSM, drug use, past STI diagnosis, and PrEP. Despite low chemsex prevalence, significantly higher proportions of chemsex users tested positive for any STI, NG anal and oral, and HIV. Future studies are needed to assess the role of chemsex in STI transmission and potential adverse interactions/effects in therapy.