The HIV/AIDS epidemics among drug injectors: a study of contact structure through a mathematical model M. Iannelli * F. A. Milner † A. Pugliese * M. Gonzo * Running title : AIDS among drug injectors in Italy This work was partially supported by: Ministero della Sanit`a - Istituto Superiore di Sanit`a - V Progetto AIDS (1992) * Dipartimento di Matematica - Universit`a di Trento, 38050, Povo (TN), Italy; Tel. 39- 461-881657; Fax 39-461-881624; E-mail: IANNELLI@SCIENCE.UNITN.IT † Department of Mathematics, Purdue University, West Lafayette, IN 47907, U.S.A.; E-mail: MILNER@MATH.PURDUE.EDU