Objectives: HIV disproportionately affects men who have sex with men (MSM). MSM and heterosexual networks are distinguished by biologically-determined sexual role segregation among heterosexuals but not MSM, and anal/vaginal transmissibility differences. We sought to identify how much these biological and demographic differences could explain persistent disparities in HIV/STD prevalence in the US, even were MSM and heterosexuals to report identical numbers of unprotected sexual partnerships per year.
Methods: We used a compartmental model parameterized using two population-based surveys. Between MSM and heterosexuals, we varied role composition (insertive-only and receptive-only vs. versatile individuals) and infectivity values.
Results: The absence of sexual role segregation in MSM and the differential anal/vaginal transmission probabilities led to considerable disparities in equilibrium prevalence. The US heterosexual population would only experience an epidemic comparable to MSM if heterosexuals' mean partner number was increased several-fold over that observed in population-based studies of either group. In order for MSM to eliminate the HIV epidemic, they would need to develop rates of unprotected sex lower than that currently exhibited by heterosexuals in the US. In our model, for US heterosexuals to have a self-sustaining epidemic, they would need to adopt levels of unprotected sex higher than currently exhibited by US MSM.
Conclusions: The persistence of disparities in HIV between heterosexuals and MSM in the US cannot be explained solely by differences in risky sexual behavior between these two populations.
- Homosexual men
- Homosexual role segregation
- Human immunodeficiency virus type 1
- Mathematical epidemiology