Purpose: Chronic infection with Hepatitis C virus (HCV) can result in fibrosis of the liver and lead to cirrhosis. In North America, the majority of new infections occur in injection drug users (IDUs). Due to the large clinical and economic burden associated with end-stage liver disease, information on the natural history of chronic HCV infection for this particular population is important to health care policy. The purpose of this study was to estimate the rate of progression to cirrhosis for those infected with HCV through injection drug use.

Methods: Articles providing information on the mean duration of infection and the prevalence of cirrhosis for those infected with HCV through injection drug use were retrieved. A fixed effects meta-analysis was performed. Information in the articles regarding co-variates such as age, sex, HIV infection, alcohol abuse, ALT levels and study population (liver clinic versus addiction therapy) were abstracted. For a subset of studies with information on all co-variates, a fixed effects meta-regression was conducted. Each analysis was based on a Poisson regression model and analyzed using Markov Chain Monte Carlo techniques with Gibbs sampling. Uninformative prior distributions were used.

Results: A total of ten articles met the inclusion and exclusion criteria. The estimated rate of progression to cirrhosis resulting from fixed effects meta-analysis was 5.1 per 1000 person-years with a 95% credible region (CR) of 4.5 to 5.6 per 1000 person-years. A subset of six studies provided information on all six co-variates. The estimated rate of progression to cirrhosis for these six studies was 1.6 per 1000 person-years (95% CR 0.6 to 3.4 per 1000 person-years). The study population type was the most important factor in estimating the risk of progression to cirrhosis, with estimates derived from liver clinic studies having a 12-fold higher progression rate compared to studies that were community-based.

Conclusions: Rates of progression to cirrhosis for those who obtained HCV infection through injection drug use are comparable to non-IDU populations. HCV prognosis depends on the study population - individuals that present to liver clinics may have faster rates of progression than those identified through addiction therapy. Unlike the non-IDU population, co-variates such as HIV infection and abuse of alcohol appear to have no effect on progression rates.