Sexual behaviour patterns in South Africa and their effect on the spread of HIV: insights from a mathematical model

Leigh Johnson, University of Cape Town
Debbie Bradshaw, Medical Research Council of South Africa
Victoria Pillay-Van Wyk, Social Aspects of HIV/AIDS and Health, Human Sciences Research Council
Thomas Rehle, Social Aspects of HIV/AIDS and Health, Human Sciences Research Council

This paper aims to quantify the effects of different types of sexual risk behaviour on the spread of HIV in South Africa. A mathematical model is developed to simulate the formation and dissolution of both spousal and non-spousal partnerships, commercial sex, and changes in coital frequency and condom usage over the life course. This is combined with a standard HIV/AIDS model, and the model is fitted to South African HIV prevalence data and sexual behaviour data. Results indicate that concurrent partnerships are a major factor driving the HIV/AIDS epidemic in South Africa, accounting for 74% (95% prediction interval: 69-78%) of new HIV infections over the 1990-2000 period. Halving unprotected sex in non-spousal relationships would reduce HIV incidence by 36% (95% prediction interval: 32-40%) over the 2010-2020 period, while changes to the rate of marriage and the frequency of commercial sex are unlikely to have a substantial impact on HIV incidence.