Abstract

To assess the incidence of and risk factors for human immunodeficiency virus (HIV) infection among HIV-negative intravenous drug abusers, we studied a cohort of intravenous drug abusers recruited from drug treatment centers in Milan and northern Italy. We enrolled 933 subjects between January 1, 1987 and April 15, 1989 and we followed 460 subjects with one or more visits for a mean follow-up duration of 10.4 months. The incidence rate of HIV infection was 7.4 per 100 person-years, equivalent to a one-year risk of 7.3%. Relative risk was higher in subjects who had been using intravenous drugs for less than 2 years (RR = 2.3). In a case-control analysis, recent frequent syringe sharing was the behavioral variable most strongly associated with HIV infection, with the highest risk in subjects sharing often (OR = 6.1, 90% CI = 2.6-14.7). We found no association with the use of cocaine in addition to heroin nor with sexual habits. Among biologic variables, relative risks were increased in individuals whose T4-lymphocyte count was lower than 1,000 at first visit (RR = 8.5, 90% CI = 2.9-24.3) or who were carrying HBsAg (RR = 1.9, 90% CI = 0.8-4.2).