A form of hepatitis caused by the hepatitis C virus (HCV), previously known as non-A, non-B hepatitis. Most infections are due to injection drug use with contaminated needles. Blood transfusion-associated infections are rarer now than in the past due to improved blood donor screening. The CDC estimates 4.1 million (1.6 percent) Americans have been infected with HCV, of whom 3.2 million are chronically infected. Of the people who have chronic hepatitis C, 10 to 20 percent eventually develop cirrhosis and one to five percent develop hepatocellular carcinoma.