Hepatitis C is a liver disease caused by the hepatitis C virus (HCV). HCV is spread primarily by exposure to human blood from an infected person. It can also be spread sexually or from an infected mother to her infant. Today, most people become infected with HCV by sharing needles or other equipment to inject drugs. Before 1992, when widespread screening of the blood supply began in the United States, HCV was also commonly spread through blood transfusions and organ transplants.