Age-dependent sexual behaviour amongst male homosexuals and the transmission dynamics of HIV-1

Abstract

The paper describes the development of an age-structured model of the transmission dynamics of HIV-1 in a male homosexual population with age-dependent rates of sexual partner acquisition, and explores the properties of the model by means of numerical methods. Age-dependency in rates of sexual partner change acts to increase the initial growth rate of the epidemic and raises the equilibrium level of endemic infection in the population when compared with the prediction of a model without age structure but with identical initial overall population mean rate of partner acquisition. In addition, age-dependency in sexual activity acts to induce demographic changes in the population where the younger more sexually active males represent an increasing proportion of the population as the epidemic develops over time. One consequence of this is an increase in the overall population mean rate of sexual partner change as a direct result of the mortality induced by AIDS in the older less sexually active classes who acquired infection at a younger age. The results are discussed in relation to the interpretation of current patterns of HIV-1 spread and the acquisition of quantitative information on sexual behaviour.