Among our sample of MSM in Lima, CAI with one or more of the last three non-transactional partners was common and associated with factors that varied according to the location where sexual contact occurred. Taken together, these findings suggest the need for a more nuanced approach to understanding the complex interaction of location type, subject and partnership characteristics, substance use, and sexual behavior in defining event-specific HIV/STI transmission risk. For example, while substance use was associated with CAI across all locations where sex occurred, the type of substance used and the “user” varied by location. Moreover, while CAI was less common in some settings compared to others, participant and partner substance use were highly associated with each other regardless of the location where sex occurred, and were variably associated with CAI in different location types. In this way, location type may be as much a part of the sexual network as the MSM connecting there, and is likely a critical part of the complex hierarchy of decisions surrounding sexual risk behavior, including cultural and network norms and individual risk psychology [32]. These findings support the differentiation of private versus public venues as contexts of sexual risk behavior, reinforce the powerful role of substance use in CAI among MSM, and highlight the potential utility of combination STI/HIV/substance use prevention techniques that can be adapted to the specific physical locations of male-male sexual interactions.

Reflecting the diversity of location-specific patterns of substance use and sexual behavior in our sample, alcohol use was associated with CAI in every type of location where sex occurred except the home, where participant marijuana use was associated with CAI. While a previous study in the U.S. identified an association between marijuana use prior to sex in commercial and public sex venues, our results suggest that the familiarity of the home environment may encourage casual drug use as well as sexual risk behavior. As a result, counseling about the risks of sex in the context of marijuana cannot be limited to MSM who attend high-risk public venues, and need to address the potential for HIV and STI transmission risk even in what are perceived as “safe” spaces [5]. These findings also emphasize the importance of the association between alcohol use and CAI found in other studies of MSM in Peru, showing that this association cuts across multiple social contexts [24, 33]. Our study is the first to identify an association between marijuana use and CAI among MSM in Peru. While there are few studies addressing the use of marijuana and sexual risk behavior among MSM worldwide, marijuana has been shown to alter judgment and impair motor coordination, and may increase the likelihood of engaging in sexual behaviors that facilitate STI and HIV transmission [34]. Future qualitative studies are needed to better understand how social environments influence the alcohol and drug use choices of MSM, how these decisions affect actual and perceived event-level risk for HIV/STI transmission, and how substance use management can be integrated with HIV/STI prevention.

Another key finding in our study was that most MSM who endorsed drug use prior to intercourse did so with two or more of their last three partners, suggesting a concentrated pattern of drug use among a sub-group of MSM. Combined with the finding that participant and partner drug use were highly correlated, our results suggest that a concerted drug use treatment intervention targeted to the highest-risk MSM could have a disproportionate, positive effect on community-level substance use. While illicit drug use among MSM in this and previous studies in Peru is only around 10%, drug use in this population has been associated with risky sexual behaviors, including high numbers of sexual partners and CAI [25]. Interventions addressing impulsive delay discounting may effectively address such risk clustering as this form of economic behavioral decision-making may have a role in both sexual risk taking and substance use [35]. A 2013 intervention in South Africa aimed towards men and their drinking environment was able to foster lasting HIV and alcohol behavior change, suggesting that interventions that address both the social environment and community norms may be capable of producing durable substance use and sexual risk behavior changes [36]. As little is known about drug use among MSM in Peru, further research is needed to characterize patterns of substance use in specific social, environmental, and partnership contexts, and to identify the different effects of specific drugs on both sexual behavior and biological vulnerability to HIV/STI acquisition and transmission in this population [37–39].

As predicted, distinct patterns of association between partner type and location of sexual contact were observed in our sample: most partners in homes and hotels were casual, and most partners in saunas/Internet cabins and public spaces were anonymous. These trends reflect the results of studies in developed countries identifying commercial sex venues as high-risk environments characterized by anonymous encounters [5]. However, our results also identify a novel area for intervention because MSM in our sample were less likely to report CAI with partners in hotels than in homes. While this finding may in part be explained by MSM inviting casual partners with whom they are more acquainted into their homes, it also highlights the danger of the perceived safety of repeat casual partners. In addition to further highlighting the potential risk of infectious disease transmission in environments perceived as “safe,” this finding also provides a more detailed understanding of the role of the site of sexual contact than previous studies of CAI and place in Latin America, which limited their analyses to commercial and/or public sex venues [12, 40]. Successful combination HIV and STI prevention interventions therefore cannot focus only on traditionally high-risk sex venues like saunas and public spaces, but must also offer MSM strategies to understand risks associated with established partners and to increase condom use in their own homes.

Finally, knowledge of partner HIV serostatus and condom conversations were highly associated in our study, underlining how effective communication skills may underpin multiple risk reduction techniques. Recent studies with MSM in Peru have revealed unacceptably low levels of HIV status communication with sexual partners [41, 42]. While there are no studies explicitly addressing rates of condom negotiation among Peruvian MSM, these conversations were reported in less than 15% of the 1341 sexual encounters in our study. Notably, serostatus conversations were associated with CAI in public sex venues. However, these conversations may have occurred as part of a process of serosorting, suggesting that these encounters were considered lower risk than those involving CAI after no discussion of serostatus. This finding contradicts a study in Portugal that found CAI with a partner whose HIV status was unknown was associated with cruising venues, and may represent a unique target for developing context-specific prevention interventions for MSM in Peru [10]. If informed by recent testing behavior, discussions of HIV serostatus prior to intercourse, even when followed by condomless intercourse, may actually reduce HIV transmission among MSM and illustrate a critical area for improvement in HIV prevention counseling for MSM in Peru [26].

Several limitations to our findings should be considered. First, our results may not be generalizable to all MSM in Lima because we collected a convenience sample of people who volunteered for a trial of rectal STI screening and combination HIV prevention. As the recruitment site is a center for community-based HIV research, our sample is likely to be higher risk, and to report a higher frequency of CAI, than the general MSM population in Peru. Second, because recent condomless receptive anal intercourse was an inclusion criterion for the trial, the sexual orientation and role of participants in our sample were primarily homosexual and pasivo or moderno. While this characteristic limits the generalizability of our results to MSM who may identify their sexual role as activo (insertive) and/or their sexual orientation as hetero- or bisexual, we were able to highlight some differences in site of sexual contact and sexual orientation to be explored in future studies. Finally, our analysis addresses only where participants had sex, and not where they met their sexual partners. As meeting place is likely to have had a significant effect on characteristics like alcohol use (e.g., if a partner was met in a bar or club), this factor may have influenced our findings on issues like substance use.