Patterns of Chemsex Substance Use and Its Association with HIV Transmission Risk Among Men Who Have Sex with Men in Thailand: A Latent Class Analysis.

Sexualized substance use or "chemsex" may contribute to the HIV epidemic among men who have sex with men (MSM) in Thailand. Specific patterns of chemsex use may be associated with different HIV/STI transmission risks. We examined typologies and correlates of sexualized substance use among a sample of high-risk MSM (n = 532) who had attended a private sex party or circuit party in the past three years using latent class analysis. Multinomial regression was used to adjust for variables associated with the 3-class latent class model. We identified a 3-class model as the best fitting model, which included: (1) "negligible sexualized substance users" (36.7%), who had never engaged in chemsex in the past six months; (2) "sexualized substance users" (13.9%), who had a high level of sexualized alcohol use and a wide range of other substances before or during sex in the past six months; and (3) "exclusive chemsex users" (49.4%), who predominantly used crystal methamphetamine, amyl nitrite, and erectile dysfunctional drugs before or during sex in the past six months. Compared to negligible sexualized substance users, exclusive chemsex users were more likely to be HIV-positive, more likely to have six or more sexual partners in the past six months, less likely to have condom use at last anal intercourse, and more likely to have provided sex work. Relative to negligible sexualized substance users, sexualized substance users reported more frequent online sex-seeking behaviors. These subgroups of Thai MSM have unique substance use patterns and HIV-related risk profiles, underscoring the importance of targeted HIV prevention strategies.