Non-injection and injection drug use and STI/HIV risk in the United States: the degree to which sexual risk behaviors versus sex with an STI-infected partner account for infection transmission among drug users.

We used the National Longitudinal Study of Adolescent Health (N = 14,322) to measure associations between non-injection crack-cocaine and injection drug use and sexually transmitted infection including HIV (STI/HIV) risk among young adults in the United States and to identify factors that mediate the relationship between drug use and infection. Respondents were categorized as injection drug users, non-injection crack-cocaine users, or non-users of crack-cocaine or injection drugs. Non-injection crack-cocaine use remained an independent correlate of STI when adjusting for age at first sex and socio-demographic characteristics (adjusted prevalence ratio (APR): 1.64, 95 % confidence interval (CI): 1.16-2.31) and sexual risk behaviors including multiple partnerships and inconsistent condom use. Injection drug use was strongly associated with STI (APR: 2.62, 95 % CI: 1.29-5.33); this association appeared to be mediated by sex with STI-infected partners rather than by sexual risk behaviors. The results underscore the importance of sexual risk reduction among all drug users including IDUs, who face high sexual as well as parenteral transmission risk.