Socio-structural and individual determinants of HIV/STI prevention behaviors in Chile: a national cross-sectional analysis

Despite ongoing prevention efforts, rates of consistent condom use and testing for human immunodeficiency virus (HIV)/sexually transmitted infections (STI) remain low in Chile. Understanding how individual and socio-structural behavioral determinants influence these prevention behaviors is essential to developing effective interventions. We analyzed nationally representative data from the ENSSEX 2022–2023 survey (n = 20,392), mapping 44 behavioral indicators to the COM-B model and the Theoretical Domains Framework. Multivariable logistic regression models assessed associations between behavioral determinants and two key outcomes: consistent condom use and HIV/STI testing, adjusted by sex and other covariates. Consistent condom use was reported by 15.5% of respondents, and HIV/STI testing by 23.1%. Injunctive norms favoring condom use were strongly associated with consistent condom use (aOR = 1.89), while access to sexual health services (aOR = 2.07) and PrEP awareness (aOR = 1.67) were strongly associated with HIV/STI testing. General knowledge about HIV was not independently associated with either behavior after adjustment. In this cross-sectional study of a nationally representative sample of Chilean adults, socio-structural factors—particularly injunctive norms and access to sexual health services—showed stronger and more consistent associations with condom use and HIV/STI testing than did knowledge-related factors after multivariable adjustment. These findings highlight the need for comprehensive, culturally tailored, multi-component interventions that integrate structural, normative, and motivational elements to enhance HIV/STI prevention in Chile and similar settings. Not applicable. ⦁ Effective HIV/STI prevention requires combining individual skills, socio-structural supports, and normative change. ⦁ Consistent condom use and HIV/STI testing remain low in Chile despite national prevention efforts. ⦁ Socio-structural determinants—including injunctive norms, access to services, and social support—exert a stronger influence on prevention behaviors than knowledge alone. ⦁ Reflective motivation and psychological capability are associated with prevention behaviors, but their effects differ by sex. ⦁ These findings identify priority targets for the design of culturally responsive behavioral interventions.