Fitting the HIV epidemic in Zambia: a two-sex micro-simulation model

• Published in: PloS one Vol. 4; no. 5; p. e5439
• Main Authors: Leclerc, Pauline M, Matthews, Alan P, Garenne, Michel L
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 05.05.2009; Public Library of Science (PLoS)
• Subjects: Acquired immune deficiency syndrome; Adults; Age; Age Factors; AIDS; Analysis; Children; Clients; Computer Science/Applications; Computer simulation; Demographics; Disease Outbreaks - statistics & numerical data; Disease susceptibility; Disease transmission; Disease Transmission, Infectious - statistics & numerical data; Epidemics; Female; Health aspects; HIV; HIV infections; HIV Infections - epidemiology; HIV Infections - transmission; Human immunodeficiency virus; Humans; Infections; Infectious Diseases/Epidemiology and Control of Infectious Diseases; Infectious Diseases/HIV Infection and AIDS; Infectious Diseases/Sexually Transmitted Diseases; Male; Marriage; Mathematical models; Mathematics/Mathematical Computing; Models, Statistical; Occupational health; Prostitution; Public Health and Epidemiology/Epidemiology; Public Health and Epidemiology/Infectious Diseases; Seroepidemiologic Studies; Serology; Sex; Sex Factors; Sexual Behavior - statistics & numerical data; Sexually transmitted diseases; Simulation; STD; Surveys; Women's Health/Sexually Transmitted Diseases; Womens health; Workers; Zambia - epidemiology; Zambia; France; Senegal; Africa
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0005439

In describing and understanding how the HIV epidemic spreads in African countries, previous studies have not taken into account the detailed periods at risk. This study is based on a micro-simulation model (individual-based) of the spread of the HIV epidemic in the population of Zambia, where women tend to marry early and where divorces are not frequent. The main target of the model was to fit the HIV seroprevalence profiles by age and sex observed at the Demographic and Health Survey conducted in 2001. A two-sex micro-simulation model of HIV transmission was developed. Particular attention was paid to precise age-specific estimates of exposure to risk through the modelling of the formation and dissolution of relationships: marriage (stable union), casual partnership, and commercial sex. HIV transmission was exclusively heterosexual for adults or vertical (mother-to-child) for children. Three stages of HIV infection were taken into account. All parameters were derived from empirical population-based data. Results show that basic parameters could not explain the dynamics of the HIV epidemic in Zambia. In order to fit the age and sex patterns, several assumptions were made: differential susceptibility of young women to HIV infection, differential susceptibility or larger number of encounters for male clients of commercial sex workers, and higher transmission rate. The model allowed to quantify the role of each type of relationship in HIV transmission, the proportion of infections occurring at each stage of disease progression, and the net reproduction rate of the epidemic (R(0) = 1.95). The simulation model reproduced the dynamics of the HIV epidemic in Zambia, and fitted the age and sex pattern of HIV seroprevalence in 2001. The same model could be used to measure the effect of changing behaviour in the future.