Changes in Blood-borne Infection Risk Among Injection Drug Users

Methods. We characterized trends in human immunodeficiency virus (HIV) and HCV infection incidence and HCV infection prevalence among injection drug users (IDUs) recruited over 4 periods: 1988-1989, 1994-1995, 1998, and 2005-2008. We calculated HIV and HCV infection incidence within the first year of follow-up among IDUs whose test results were negative for these viruses at baseline (n = 2061 and n = 373, respectively). We used Poisson regression to compare trends across groups. Results. HIV infection incidence declined significantly from 5.5 cases/100 person-years (py) in the 1988-1989 group to 2.0 cases/100 py in the 1994-1995 group to 0 cases/100 py in the 1998 and 2005-2008 groups. Concurrently, HCV infection incidence declined but remained robust (22.0 cases/100 py in the 1988-1989 cohort to 17.2 cases/100 py in the 1994-1995 cohort, 17.9 cases/100 py in the 1998 cohort, and 7.8 cases/100 py in the 2005-2008 cohort; P = .07). Likewise, HCV infection prevalence declined, but chiefly in younger IDUs. For persons aged < 39 years, relative to the 1988-1989 cohort, all groups exhibited significant declines (adjusted prevalence ratio [PR] for the 2005-08 cohort, .73; 95% confidence interval [CI], .65-.81). However, for persons aged >= 39 years, only the 2005-2008 cohort exhibited declining prevalence compared with the 1988-1989 cohort (adjusted PR, .87; 95% CI, .77-.99). Conclusions. Although efforts to reduce blood-borne infection incidence have had impact, this work will need to be intensified for the most transmissible viruses, such as HCV.