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Although numerous studies have examined sexual and substance use behaviors that put people at risk for sexually transmitted infections including HIV, most focus on an overall measure of aggregate risk or a few simple and particular subtypes of sexual acts assessed in separate analyses. In this article, we introduce a more sensitive approach to assess how the relative characteristics of sex acts may determine the level of risk in which an individual chooses to engage. Project AWARE, a randomized clinical trial conducted among 5012 patients in nine STD clinics across the U.S., is used to illustrate the approach. Our study was guided by two aims: (1) describe a new approach to examine the count of sexual acts using a disaggregated repeated measures design and (2) show how this new approach can be used to evaluate interactions among different categories of sexual risk behaviors and other predictors of interest (such as gender/sexual orientation). Profiles of different subtypes of sexual acts in the past 6 months were assessed. Potential interactions of the characteristics associated with each subtype which resulted in up to 48 distinct subtypes of sexual risk behaviors-sex with a primary/non-primary partner; partner's HIV status; vaginal/anal sex; condom use; and substance use before or during sex act-can be examined. Specifically, we chose condom use and primary and non-primary status of partner as an application in this paper to illustrate our method. There were significantly more condomless sex acts (M = 23, SE = 0.9) and sex acts with primary partners (M = 27.1, SE = 0.9) compared to sex acts with condoms (M = 10.9, SE = 0.4, IRR = 2.10, 95% CI 1.91-2.32, p < .001) and sex acts with non-primary partner (M = 10.9, SE = 0.5, IRR = 2.5, 95% CI 2.33-2.78, p < .001). In addition, there were significant differences for the count of sexual risk behaviors among women who have sex with men (WSM), men who have sex with women (MSW) and men who have sex with men (MSM) for sex acts with and without condom use, primary and non-primary partner, and their interaction (ps = .03, < .0001, and .001, respectively). This approach extends our understanding of how people make choices among sexual behaviors and may be useful in future research on disaggregated characteristics of sex acts.

This study examined differences in sexual risk behaviors by gender and over time among 1281 patients (777 males and 504 females) from 12 community-based substance use disorder treatment programs throughout the United States participating in CTN-0032, a randomized control trial conducted within the National Drug Abuse Treatment Clinical Trials Network. Zero-inflated negative binomial and negative binomial models were used in the statistical analysis. Results indicated significant reductions in most types of sexual risk behaviors among substance users regardless of the intervention arms. There were also significant gender differences in sexual risk behaviors. Men (compared with women) reported more condomless sex acts with their non-primary partners (IRR = 1.80, 95 % CI 1.21-2.69) and condomless anal sex acts (IRR = 1.74, 95 % CI 1.11-2.72), but fewer condomless sex partners (IRR = 0.87, 95 % CI 0.77-0.99), condomless vaginal sex acts (IRR = 0.83, 95 % CI 0.69-1.00), and condomless sex acts within 2 h of using drugs or alcohol (IRR = 0.70, 95 % CI 0.53-0.90). Gender-specific intervention approaches are called for in substance use disorder treatment.