The hepatitis C virus (HCV) is one of the most important causes ofchronic liver disease in the United States. It accounts for about 20 percent of acute viral hepatitis, 60 to 70 percent of chronic hepatitis, and 30 percent of cirrhosis, end-stage liver disease, and liver cancer. Almost 4 million Americans, or 1.8 percent of the U.S. population, are infected with HCV. Hepatitis C causes an estimated 8,000 to 10,000 deaths annually in the United States.

A distinct and major characteristic of hepatitis C is its propensity to cause chronic liver disease. At least 75 percent of patients with acute hepatitis C ultimately develop chronic infection, and most of these patients have accompanying chronic liver disease.

Chronic hepatitis C varies greatly in its course and outcome. At one end of the spectrum are patients who have no signs or symptoms of liver disease and completely normal levels of serum liver enzymes. Liver biopsy usually shows some degree of chronic hepatitis, but the degree of injury is usually mild and the overall prognosis may be good. On the other end of the spectrum are patients with severe hepatitis C who have symptoms, HCV RNA in serum, and elevated serum liver enzymes, and who ultimately develop cirrhosis and end-stage liver disease. In the middle of the spectrum are many patients who have few or no symptoms, mild to moderate elevations in liver enzymes, and a prognosis that is uncertain. The best estimates are that at least 20 percent of patients with chronic hepatitis C develop cirrhosis, a process that generally takes 10 to 20 years. After 20 to 40 years, a smaller percentage of patients with chronic disease develop liver cancer.

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