Background. Population-level hepatitis C virus (HCV) infection incidence is a surrogate for community drug-related risk.
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.
Figure 1. Incidence per 100 person-years of human immunodeficiency virus and hepatitis C virus infection by recruitment cohort in the AIDS Linked to the Intravenous Experience (ALIVE) cohort, 1988–2009.
Figure 2. Hepatitis C virus infection prevalence by age at entry and recruitment cohort in the AIDS Linked to the Intravenous Experience (ALIVE) cohort, 1988–2008 (n = 1731).
Figure 3. Prevalence ratios of hepatitis C virus infection by recruitment cohort for persons aged <39 years and persons aged ≥39 years. Results are from Poisson regression with robust variance estimates are stratified by age because there was a statistically significant interaction between age and recruitment cohort (P < .01). Panel A reflects ages of <39 years and panel B reflects ages of ≥39 years. The reference group for all models is the 1988–1989 cohort. P values for all prevalence ratios in panel A are statistically significant. Only the P value for the 2005–2008 cohort in model 2 of panel A is statistically significant. Age was included as a continuous variable in both models to account for residual confounding. Drug-related risk behaviors include lifetime history of needle sharing, shooting gallery attendance, and drug treatment; sexual risk behavior includes number of sexual partners in the preceding 10 years.