Background:  National statistics suggest declining HIV incidence among IDUs over the past two decades. Whether there have been comparable trends in other blood-borne infections (e.g. HCV) is unclear but has implications for resource allocation, prevention interventions and vaccine studies. We characterize HCV prevalence and incidence in a cohort of IDU over 20 years, where we have previously demonstrated declining HIV incidence (4.4 per 100 patient-years in 1988 to 1989 to 0.20 per 100 patient-years in 2005 to 2008).

Methods:  ALIVE is an ongoing cohort of IDU in Baltimore, MD. We characterized trends in HCV prevalence among 1698 IDU recruited in 4 periods: 1988 to 1989, 1994 to 1995, 1997, and 2005 to 2008. Incidence per 100 person-years was calculated over the first 2 years of follow-up for those in each recruitment cohort who were HCV antibody negative at entry (n = 373). Trends were compared across the 4 groups using Poisson regression.

Results:  At recruitment, median age was 39 years, 77% were female, 78% black and 20% HIV positive. HCV prevalence declined from 85% in 1988 to 1989 to 78% in 1994 to 1995, and 70% in 1998, but increased to 78% in 2005 to 2008 (P <0.01). Similarly, HCV incidence declined from 13.2 per 100 patient-years in 1988 to 1989 to 7.1 per 100 patient-years in 1994 to 1995 and 4.4 in 1998, but again increased to 8.5 per 100 patient-years in 2005 to 2008 (P <0.01). However, after adjusting for age, years of injection drug use, other demographics and drug-related risk behaviors, the prevalence and incidence in 2005 to 2008 were comparable to 1998 suggesting that the apparent increase was due to differences between the cohorts. In multivariate analyses, all groups exhibited declines in incidence from the original cohort (incidence rate ratio [IRR] 1994 to 1995, 0.48; 95%CI 0.22 to 1.1; IRR 1997 to 1998, 0.22; 95%CI 0.07 to 0.65; IRR 2005 to 2008, 0.20; 95%CI 0.05 to 0.72) and there was suggestion of further reduction from 1994 to 1995 to 1998 (IRR 0.47). Decreases were observed in both HIV positive and negative IDU; however, there was a more dramatic decrease in prevalence among HIV positives that continued even after 1998 (prevalence ratio for 2005 to 2008 vs 1999, 0.92).

Conclusions:  These data suggest that commensurate with HIV infection, HCV prevalence and incidence have declined among IDUs with the most substantial change coming before 1998. However, a 78% prevalence and an incidence more than 40-fold higher than HIV in 2005 to 2008 reflects continued high levels of transmission and a large future burden of HCV-associated liver disease among IDU with and without HIV.