Hepatitis C virus (HCV) infection is the most common chronic bloodborne infection in the United States. CDC staff estimate that during the 1980s, an average of 242,000 new infections occurred each year. Since 1989, the annual number of new infections has declined by >80% to 36,000 by 1996. Data from the Third National Health and Nutrition Examination Survey (NHANES III), conducted during 1988–1994, have indicated that an estimated 3.9 million (1.8%) Americans have been infected with HCV.   Most of these persons are chronically infected and might not be aware of their infection because they are not clinically ill. Infected persons serve as a source of transmission to others and are at risk for chronic liver disease or other HCV-related chronic diseases during the first two or more decades following initial infection.

Chronic liver disease is the tenth leading cause of death among adults in the United States, and accounts for approximately 25,000 deaths annually, or approximately 1% of all deaths. Population-based studies indicate that 40% of chronic liver disease is HCV-related, resulting in an estimated 8,000–10,000 deaths each year. Current estimates of medical and work-loss costs of HCV-related acute and chronic liver disease are >$600 million annually, and HCV- associated end-stage liver disease is the most frequent indication for liver transplantation among adults. Because most HCV-infected persons are aged 30–49 years, the number of deaths attributable to HCV- related chronic liver disease could increase substantially during the next 10–20 years as this group of infected persons reaches ages at which complications from chronic liver disease typically occur.

HCV is transmitted primarily through large or repeated direct percutaneous exposures to blood. In the United States, the relative importance of the two most common exposures associated with transmission of HCV, blood transfusion and injecting-drug use, has changed over time. Blood transfusion, which accounted for a substantial proportion of HCV infections acquired >15 years ago, rarely accounts for recently acquired infections. Since 1994, risk for transfusion-transmitted HCV infection has been so low that CDC’s sentinel counties viral hepatitis surveillance system has been unable to detect any transfusion-associated cases of acute hepatitis C, although the risk is not zero. In contrast, injecting-drug use consistently has accounted for a substantial proportion of HCV infections and currently accounts for 60% of HCV transmission in the United States. A high proportion of infections continue to be associated with injecting-drug use, but for reasons that are unclear, the dramatic decline in the incidence of acute hepatitis C since 1989 correlates with a decrease in cases among injecting-drug users.

Reducing the burden of HCV infection and HCV-related disease in the United States requires implementation of primary prevention activities to reduce the risk for contracting HCV infection and secondary prevention activities to reduce the risk for liver and other chronic diseases in HCV-infected persons. Figure 1

BACKGROUND
Prospective studies of transfusion recipients in the United States demonstrated that rates of posttransfusion hepatitis in the 1960s exceeded 20%. In the mid-1970s, available diagnostic tests indicated that 90% of posttransfusion hepatitis was not caused by hepatitis A or hepatitis B viruses and that the move to all-volunteer blood donors had reduced risks for posttransfusion hepatitis to 10%. Although non-A, non-B hepatitis (i.e., neither type A nor type B) was first recognized because of its association with blood transfusion, population-based sentinel surveillance demonstrated that this disease accounted for 15% to 20% of community-acquired viral hepatitis in the United States. Discovery of HCV by molecular cloning in 1988 showed that non-A, non-B hepatitis was primarily caused by HCV infection.