Homosexual role separation: Implications for analyzing and modeling the spread of HIV

The analysis of the spread of HIV in homosexual populations must be based on knowledge of all factors which promote or inhibit transmission. Recently, data were reported from the Amsterdam cohort study that imply that sexual role separation and the changes therein should be taken into account in analyzing and modeling the spread of HIV. In this paper, a role separation mixing model is described and linked to data from the Amsterdam cohort. The model allows one to study the impact of homosexual role separation on the spread of HIV. The homosexual men are classified into four sexual subgroups based on the preference for: 1) no anal intercourse; 2) anal insertive only; 3) anal receptive only; 4) both insertive and receptive. The analysis accounts for variability and change in homosexual role behavior and loss to follow up. The results support the conjecture that there are large differences between the risks of receptive and insertive anal intercourse, with the latter carrying only minimal risk. The analysis indicates that the spread of HIV is mostly restricted to subgroup 4, the largest and sexually most active subgroup. In this subgroup, the estimated probability of HIV transmission from an infected insertive partner (in subgroup 2 or 4) to a receptive susceptible (in subgroup 4) is between 1 and 5 percent (assuming a closed cohort).