Regional distributions of chemsex, broader sexualised substance use and individual-level substance use patterns and their associations with HIV among men who have sex with men in the Netherlands: a Bayesian spatial ecological modelling and a latent class analysis.

BACKGROUND

Chemsex increases HIV risk, but the Dutch substance landscape is evolving beyond traditional drugs (e.g. GHB/GBL, methamphetamine) to include novel synthetic cathinones. This study mapped the spatial distribution of sexualised substance use and identified distinct chemsex-user profiles among men who have sex with men (MSM) in the Netherlands.

METHODS

Data from 1413 Dutch MSM in the EMIS-2024 survey (December 2023-July 2024) were analysed. Bayesian spatial ecological regression estimated the regional posterior prevalence and relative risk (RR) of chemsex engagement and its association with regional self-reported HIV prevalence. Latent-class analysis (LCA) identified substance-use patterns. Logistic regression assessed associations between HIV, chemsex engagement, and user patterns.

RESULTS

Overall, 19.8% of MSM reported chemsex. Regional prevalence was highly heterogeneous, ranging from 25.2% (RR = 1.27) in GGD-Amsterdam to 16.4% (RR = 0.83) in GGD IJsselland. Amsterdam and unexpected border regions (e.g. GGD-Drenthe) showed significantly higher RRs for chemsex engagement and the broader sexualised substance use. Substance use varied widely, with a notable presence of novel synthetic stimulants (13.9%) and ecstasy (21.4%). LCA revealed two distinct profiles: a 'Traditional Substance-Moderate use' class and a 'Broader-Polysubstance' class using a broader range of sexualised substances. Both individual and ecological analyses confirmed a strong association between chemsex engagement and higher self-reported HIV prevalence.

CONCLUSION

Chemsex among Dutch MSM is geographically heterogeneous and increasingly features broad polysubstance use. Its consistent link to higher self-reported HIV prevalence at individual and regional levels highlights the need for geographically tailored harm-reduction strategies.