A Data-Driven Simulation of HIV Spread Among Young Men Who Have Sex With Men: Role of Age and Race Mixing and STIs

Abstract

Objective: Young men who have sex with men (YMSM) in the United States have a high HIV incidence with substantial racial disparities that are poorly understood. We use a data-driven simulation model to understand the impact of network-level mechanisms and sexually transmitted infections on the spread of HIV among YMSM.

Methods: We designed and parameterized a stochastic agent-based network simulation model using results of a longitudinal cohort study of YMSM in Chicago. Within this model, YMSM formed and dissolved partnerships over time, and partnership types were stratified by length of partnership, sex, and age of the partner. In each partnership, HIV, gonorrhea, and chlamydia could be transmitted. Counterfactual scenarios were run to examine drivers of HIV.

Results: Over a 15-year simulation, the HIV epidemic among YMSM continued to rise, with Latino/white YMSM facing a steeper increase in the HIV burden compared with black YMSM. YMSM in partnerships with older MSM, in particular black YMSM with older black MSM, were at highest risk for HIV, and 1 infection prevented with an older partner would prevent 0.8 additional infections among YMSM. Additionally, racial disparities in HIV were driven by differences in the HIV prevalence of YMSM partners. Finally, of all HIV infections among YMSM, 14.6% were attributable to NG and CT infections.

Conclusion: Network-level mechanisms and sexually transmitted infections play a significant role in the spread of HIV and in racial disparities among YMSM. HIV prevention efforts should target YMSM across race, and interventions focusing on YMSM partnerships with older MSM might be highly effective.

Figure 1

Simulated HIV prevalence (Figure 1A) and incidence per 100 person-years (Figure 1B) stratified by race over 15 years. Figure 1B shows the mean HIV incidence per 100 person-years per time-step (i.e., 0.5 months) with the half-width of the 95% CI are ≤3.5% of the mean except for Other YMSM.

Figure 2

Simulated new HIV infections per 100 person-years over 15 years among YMSM stratified by race and relationship type. “Total “ shows the simulated number of total HIV infections that occurred in all sexual relations. “One-night “: simulated new HIV infections that occurred in one-night-partnerships; “Outside “: simulated new HIV infections that occurred in outside-partnerships, i.e. with older male or female partners. HIV infections from females was rare. In outside partnerships with females, 0.0049 HIV infections per 100 person-years (95% CI: 0.0040–0.0057) occurred. In one-night-partnerships with females, 0.0035 (95% CI: 0.0029–0.0041) occurred. “Within “: simulated new HIV infections that occurred in within-partnerships, i.e. partnerships with other YMSM.

Figure 3

HIV infections per 100 partnership-years, male-male partnerships only. A) Base-case scenario corresponding to Figures 1 and 2. HIV infections per 100 male-male partnership-years in case of one-night-partnerships denotes HIV infections per average number of one-night-partnerships per year. For within-partnerships the number of partnership-years is the sum of the number of susceptible-infected partnership-years plus two times the number of susceptible-susceptible partnership-years (see online Appendix section 7.2 for details). B) Counterfactual scenario with no race-assortative mixing, i.e. YMSM select partners independent of race. C) Counterfactual scenario with no difference by race in initial HIV prevalence (5.6% at baseline) and among outside partners (set to 17.2%). D) Counterfactuals of Figures B) and Figure C) combined. In case of outside partnerships, i.e. partnerships of YMSM with older MSM, Black-NonBlack partnerships denote both partnerships of Black YMSM with older NonBlack MSM and partnerships of NonBlack YMSM with older Black MSM (see also Figure 27 in online Appendix section SDC 7.2).

Figure 4

HIV prevalence stratified by race and total number of new HIV infections over 15 years (Figure 4D) for the base-case scenario (Figure 4A) corresponding to Figures 1 and 2, for a counterfactual scenario where no HIV transmission occurs in outside partnerships of YMSM with older MSM or females (Figure 4C); and for a counterfactual scenario where HIV transmission risk in outside partnerships is reduced by 50% compared to the base-case scenario (Figure 4B). HIV infections from females was rare, see also caption of Figure 2.