INFECTION WITH HIV AND HEPATITIS-C-VIRUS AMONG INJECTING DRUG-USERS IN A PREVENTION SETTING - RETROSPECTIVE COHORT STUDY

Objectives: To estimate the incidence of HIV and hepatitis C virus and risk factors for seroconversion among a cohort of injecting drug user s. Design: Retrospective cohort study. Setting: Primary healthcare fac ility in central Sydney. Subjects: Injecting drug users tested for HIV -1 antibody (n = 1179) and antibodies to hepatitis C virus (n = 1078) from February 1992 to October 1995. Main outcome measures: Incidence o f HIV-1 and hepatitis C virus among seronegative subjects who injected drugs and underwent repeat testing. Demographic and behavioural risk factors for hepatitis seroconversion. Results: Incidence of HIV-1 amon g 426 initially seronegative injecting drug users was 0.17/100 person years (two seroconversions) compared with an incidence of hepatitis C virus of 20.9/100 person years (31 seroconversions) among 152 injectin g drug users initially negative for hepatitis C virus. Incidence of he patitis C virus among injecting drug users aged less than 20 years was 75.6/100 person years. Independent risk factors for hepatitis C virus seroconversion were age less than 20 years and a history of imprisonm ent. Conclusions: In a setting where prevention measures have contribu ted to the maintenance of low prevalence and incidence of HIV-1, trans mission of hepatitis C virus continues at extremely high levels, parti cularly among young injecting drug users.