THE HIV AIDS EPIDEMICS AMONG DRUG INJECTORS - A STUDY OF CONTACT STRUCTURE THROUGH A MATHEMATICAL-MODEL/

Numerical results of a model with variable infectivity for the dynamic s of HIV/AIDS (human immunodeficiency virus/acquired immune deficiency syndrome) have been compared with the data of AIDS cases among intrav enous drug users in Italy, especially in the Latium region. We examine d several hypotheses about the dynamics of the epidemics; for each we obtained, mainly through a least-square approach but also minimizing a different quantity, a best-fit estimate of the parameters. In the sim plest model, the population is assumed to be homogeneous, and we estim ate contact rate and year of start of the epidemics, obtaining a good fit up to 1989, less so after. A substantial increase in fit is obtain ed in assuming either a decrease of the contact rate over time or a he terogeneous population with a smaller active group. We have also compa red models with different infectivity curves during the incubation per iod: the assumption of constant infectivity is untenable, whereas the often suggested hypothesis of a peak in infectivity shortly after infe ction seems to be in agreement with data. (C) Elsevier Science Inc, 19 97