Examining HIV risk and prevention behaviors among men who have sex with men in Ending the HIV Epidemic states in the Western US region between 2017 and 2021: a serial-cross-sectional analysis of the American Men’s Internet Survey

BACKGROUND: The Western region of the US has received comparatively less attention in HIV research despite housing several Ending the HIV Epidemic priority areas. Understanding HIV risk and prevention behaviors among men who have sex with men (MSM) in this region is critical. This study examines differences in HIV risk and prevention behaviors among MSM in the Pacific (CA, WA) and Mountain (AZ, NV) sub-regions. METHODS: We conducted a serial cross-sectional analysis using 2017-2021 data from the American Men's Internet Survey. The sample included MSM with HIV-negative or unknown status. Key outcomes included condomless anal intercourse, substance use, STI diagnoses, HIV/STI testing, and PrEP awareness, willingness and use. Poisson regression models with robust standard errors estimated prevalence ratios and 95% confidence intervals, adjusting for sociodemographics. RESULTS: Among 7423 MSM, 81.3% resided in the Pacific sub-region, 53.0% were aged