Abstract
In this work, we estimate the proportions of transmissions occurring in main vs. casual partnerships, and by the sexual role, infection stage, and testing and treatment history of the infected partner, for men who have sex with men (MSM) in the US and Peru. We use dynamic, stochastic models based in exponential random graph models (ERGMs), obtaining inputs from multiple large-scale MSM surveys. Parallel main partnership and casual sexual networks are simulated. Each man is characterized by age, race, circumcision status, sexual role behavior, and propensity for unprotected anal intercourse (UAI); his history is modeled from entry into the adult population, with potential transitions including HIV infection, detection, treatment, AIDS diagnosis, and death. We implemented two model variants differing in assumptions about acute infectiousness, and assessed sensitivity to other key inputs. Our two models suggested that only 4–5% (Model 1) or 22–29% (Model 2) of HIV transmission results from contacts with acute-stage partners; the plurality (80–81% and 49%, respectively) stem from chronic-stage partners and the remainder (14–16% and 27–35%, respectively) from AIDS-stage partners. Similar proportions of infections stem from partners whose infection is undiagnosed (24–31%), diagnosed but untreated (36–46%), and currently being treated (30–36%). Roughly one-third of infections (32–39%) occur within main partnerships. Results by country were qualitatively similar, despite key behavioral differences; one exception was that transmission from the receptive to insertive partner appears more important in Peru (34%) than the US (21%). The broad balance in transmission contexts suggests that education about risk, careful assessment, pre-exposure prophylaxis, more frequent testing, earlier treatment, and risk-reduction, disclosure, and adherence counseling may all contribute substantially to reducing the HIV incidence among MSM in the US and Peru.
Highlights
The HIV epidemic in the United States and other highly developed nations remains concentrated among men who have sex with men (MSM), with over half of new infections occurring in this community [1]
The US prevalence estimate is slightly higher than the 25% found in most cities in the first MSM round of NHBS [44], an expected pattern given that most source datasets excluded MSM with no HIV risk
Given the divergence between our estimates of the proportion of transmissions occurring in main partnerships and other published estimates, we explored the impact of different assumptions about the relative frequency of unprotected anal intercourse (UAI) in main partnerships versus casual contacts (Figure 4b)
Summary
The HIV epidemic in the United States and other highly developed nations remains concentrated among men who have sex with men (MSM), with over half of new infections occurring in this community [1]. In the US, HIV incidence is rising among young MSM, especially Blacks [3]. Incidence trends for Latin American MSM are less well characterized, prevalence remains high in this community throughout the region [4]. Recent advances in pre-exposure prophylaxis [5], testing [6], antiretroviral treatment-as-prevention [7] and circumcision [8,9,10] have raised hopes for HIV prevention, including among MSM. While none alone is likely to stop the epidemic, larger reductions in incidence may be achieved by prevention packages, tailored to individual risks and preferences, that combine some or all of these new interventions with new and existing counseling approaches that support adherence, more frequent HIV testing, and continued sexual risk reduction
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