Risk behaviour change and HIV infection among injection drug users in Montreal.

Objective: To investigate the independent association between changes in risk behaviour and HIV seroconversion risk among Montreal injection drug users (IDU).

Design: A longitudinal study of risk behaviour change and the maintenance of low-risk practices. At baseline and semi-annually, subjects were tested for HIV, and questionnaires on risk behaviour were completed.

Results: A total of 833 IDU were recruited from January 1992 to June 1998, and completed a minimum of three visits. Large fluctuations in risk behaviour were observed, and the risk of HIV infection appeared to be dependent upon the consistency of risk behaviour practised. IDU who consistently engaged in risky behaviour were at high risk of HIV infection. IDU who attempted to practise low-risk behaviour but experienced relapses to risky behaviour were also at considerable risk of infection. IDU who managed to maintain low-risk practices were at minimal risk. Using Cox regression analysis, the hazard ratio (HR) of HIV seroconversion among IDU who consistently and inconsistently shared needles with an HIV-positive partner was 8.17 (95% CI 3.59-18.59) and 2.63 (95% CI 1.33-5.17), respectively, relative to non-needle sharers. Corresponding HIV incidence rates were 30.42 per 100 person-years (py) among consistent sharers, 13.78 per 100 py among inconsistent sharers and 2.51 per 100 py among non-sharers.

Conclusion: Although some HIV risk reduction was evident, behaviour change seems to be effective only in IDU who adopt and maintain low-risk practices. Additional strategies may be needed to assist IDU in the maintenance of low-risk practices.