HIV and hepatitis C virus risk in new and longer-term injecting drug users in Oslo, Norway.

Research has focused on understanding injecting drug use initiation in the era of HIV/AIDS. However, differences between new and longer-term injecting drug users (IDUs) have not received as much attention. This study examined injecting initiation experience, risk and risk reduction practices, and self-reported HIV and hepatitis C virus (HCV) testing practices and infection among new (injecting < or =4 years) and longer-term IDUs. Data from 3 cross-sectional surveys in 1992, 1994, and 1997 of syringe exchange program (SEP) users in Oslo, Norway, were used. Approximately one fifth of IDUs were new injectors. New IDUs were increasingly indistinguishable from longer-term IDUs in terms of socio-demographics, risk practices, and HIV and HCV testing. The prevalence of HIV infection remained low (5%); in contrast, approximately two thirds of all SEP users reported being HCV-infected. Known HCV infection status had no impact on syringe sharing; most HCV-infected SEP users reported sharing syringes, regardless of the duration of injecting. The only variable associated with HCV infection was injecting < or =4 years (adjusted odds ratio = 0.2; 95% confidence interval = 0.1-0.4). Increased similarity in age between new and longer-term IDUs may have contributed to the rapid spread of HCV infection by facilitating mixing patterns between HCV-infected and -susceptible IDUs.