Background: The prevalence of hepatitis C virus (HCV) infection in the United States has remained constant from 1988 through 2002, although the peak age of infection has increased. While the number of new HCV cases is declining, the rates of HCV-associated morbidity and mortality are increasing. We reviewed the risk factors for HCV infection, the laboratory methods used to diagnose it, the dynamics of disease progression, and the natural history of HCV infection.

Methods: Medline searches were performed using the key word HCV, together with incidence, risk factors, demographics, diagnostic methods, disease progression, natural history, normal alanine aminotransferase (ALT), fibrosis, and hepatocellular carcinoma (HCC).

Results: Three characteristics-abnormal serum ALT, history of injection drug use, and blood transfusion before 1992-identified 85% of HCV-positive individuals 20-59 years old. About 75%-85% of acutely infected individuals progress to chronic infection, with up to 20% developing liver cirrhosis over 20-25 years, putting them at increased risk for end-stage liver disease and/or HCC. HCV-associated cirrhosis is the leading cause of liver transplantation in the United States. Rates of infection are higher in non-Hispanic blacks than in non-Hispanic whites and Mexican Americans and higher in men than in women. In the United States, over 70% of HCV-infected individuals are infected with genotype 1.

Conclusions: HCV infection is more prevalent than human immunodeficiency virus or hepatitis B virus infection and is particularly common among certain demographic groups. Individual rates of fibrosis progression vary, but identification of host and viral characteristics associated with disease progression may reveal the mechanisms of HCV-associated hepatic fibrosis/cirrhosis.