Incidence and risk factors for hepatitis C seroconversion in injecting drug users in Australia

To determine the incidence of hepatitis C virus (HCV) infection and identify risk factors for seroconversion.

Prospective cohort study. Participants were recruited through direct approaches, street-based outreach, methadone and sexual health clinics and needle and syringe programmes.

Urban, regional and rural settings in New South Wales, Australia.

Injecting drug users (IDUs) (n = 584) were screened and tested for exposure to HCV. Between 1999 and 2002 antibody HCV negative IDUs (n = 368) were enrolled and followed-up every 3-6 months until seroconversion or study completion.

Interviewer-administered baseline and follow-up questionnaires consisted of 131 items and included demographics, drug use and risk behaviour. Approximately 10 cc of whole blood was drawn at each visit. Specimens were stored at -70C and serology performed using one or two third-generation enzyme-linked immunosorbent assays and polymerase chain reaction testing.

Sixty-eight seroconversions were observed and incidence was 30.8 per 100 person-years, with incidence in IDUs injecting < 1 year, 133 per 100 person-years. Independent predictors of seroconversion were female gender, duration of injecting, injecting cocaine, shared use of filters and recruitment strategy.

Women, new initiates and IDUs recruited via outreach appear to be at increased risk of infection. Results confirm the significance of cocaine injection as a risk factor and provide the first evidence outside North America of the link between shared use of drug preparation equipment and incident HCV infection. Prevention efforts should attempt to raise awareness of the risks associated with drug sharing and, in particular, the role of potentially contaminated syringes in HCV infection.