Prevalence and incidence of HIV among out-of-treatment injecting drug users, Chicago 1994-1996

Objectives: To assess HIV prevalence, incidence, and associated risk factors among IDUs in Chicago. Methods: Seven hundred ninety-four street-recruited IDUs ranging in age from 18 to 50 years, who were not in drug treatment at study enrollment, were interviewed and tested for HIV at baseline and at two follow-ups scheduled 6 and 12 months after baseline. Questionnaires assessed respondents' demographic characteristics, medical and drug treatment histories, drug use, and sexual practices. Results: HIV seroprevalence at baseline was 18%. Logistic regression identified the following determinants of prevalent HIV infection: Puerto Rican ethnicity, homosexual or bisexual self-identification, injecting for 4 or more years, and having smoked crack cocaine in the past 6 months. Follow-up data were collected from 584 (73.6%) participants. Mean duration of follow-up was 16.5 months, indicating that most subjects had follow-up intervals longer than the scheduled 6 and 12 months. Seven HIV seroconversions were observed in 632 person years of risk, yielding an incidence rate of 1.1 per 100 person years of risk. Injection for 3 or less years was positively associated with HIV seroconversion. Conclusions: The findings provide evidence of a decline in HIV incidence among IDUs, though newer injectors remain at elevated risk for infection.