Chapter 8: Modelling the HIV-1 and AIDS Epidemic among Drug Injectors.

The article focuses on the uses of mathematical models in the analysis of HIV-1 and AIDS epidemic among drug injectors. The article stresses two aims of mathematical modelling. The first is to identify and to quantify the importance of the main routes through which the spread of HIV-1 infections are likely to have occurred and to occur in the near future; the second aim is to perform "thought experiments" on possible or conceivable control programmes. The article develops a conceptual tool, aimed to improve the understanding of the transmission dynamics of HIV-1 in populations where drug injectors represent a significant reservoir of infection. Using this tool, and an estimate of the Lazio prevalence scenario at the beginning of 1991, the article estimates the amount of infections acquired in the first years of this decade by IDUs and NDIHs, with respect to sex and transmission route. It then predicts the epidemic trends up to the year 2000, and performs a "thought experiment," in a field where a real experiment would have been simply impossible, obtaining results which strongly suggest priorities for prevention programmes.