• identify new cases and determine disease incidence and trends;
• determine risk factors for infection and disease transmission patterns;
• estimate disease burden; and
• identify infected persons who can be counseled and referred for medical follow-up.

Various surveillance approaches are required to achieve these objectives because of limitations of diagnostic tests for HCV infection, the number of asymptomatic patients with acute and chronic disease, and the long latent period between infection and chronic disease outcome.

Surveillance for Acute Hepatitis C
Surveillance for acute hepatitis C -- new, symptomatic infections -- provides the information necessary for determining incidence trends, changing patterns of transmission and persons at highest risk for infection.  In addition, surveillance for new cases provides the best means to evaluate effectiveness of prevention efforts and to identify missed opportunities for prevention. Acute hepatitis C is one of the diseases mandated by the Council of State and Territorial Epidemiologists (CSTE) for reporting to CDC's National Notifiable Diseases Surveillance System.  However, hepatitis C reporting has been unreliable to date because most health departments do not have the resources required for case investigations to determine if a laboratory report represents acute infection, chronic infection, repeated testing of a person previously reported, or a false-positive result.  Historically, the most reliable national data regarding acute disease incidence and transmission patterns have come from sentinel surveillance (i.e., sentinel counties study of acute viral hepatitis). As hepatitis C prevention and control programs are implemented, federal, state, and local agencies will need to determine the best methods to effectively monitor new disease acquisition.

Laboratory Reports of Anti-HCV-Positive Tests
Although limitations exist for the use of anti-HCV- positive laboratory reports to identify new cases and to monitor trends in disease incidence, they potentially are an important source from which state and local health departments can identify infected persons who need counseling and medical follow-up. Development of registries of persons with anti-HCV-positive laboratory results might facilitate efforts to provide counseling and medical follow-up and these registries could be used to provide local, state, and national estimates of the proportion of persons with HCV infection who have been identified. If such registries are developed, the confidentiality of individual identifying information should be ensured according to applicable laws and regulations.

Serologic Surveys
Serologic surveys at state and local levels can characterize regional and local variations in prevalence of HCV infection, identify populations at high risk, monitor trends, and evaluate prevention programs. Existing laboratory-based reporting of HCV-positive test results cannot provide this information because persons who are tested will not be representative of the population as a whole, and certain populations at high risk might be under represented. Thus, data from newly designed or existing serologic surveys will be needed to monitor trends in HCV infection and evaluate prevention programs at state and local levels.

Surveillance for Chronic Liver Disease
Surveillance for HCV-related chronic liver disease can provide information to measure the burden of disease, determine natural history and risk factors, and evaluate the effect of therapeutic and prevention measures on incidence and severity of disease. Until recently, no such surveillance existed, but a newly established sentinel surveillance pilot program for physician-diagnosed chronic liver disease will provide baseline data and a template for a comprehensive sentinel surveillance system for chronic liver disease. As the primary source of data regarding the incidence and natural history of chronic liver disease, this network will be pivotal for monitoring the effects of education, counseling, other prevention programs, and newly developed therapies on the burden of the disease.

FUTURE DIRECTIONS
To prevent chronic HCV infection and its sequelae, prevention of new HCV infections should be the primary objective of public health activities. Achieving this objective will require the integration of HCV prevention and surveillance activities into current public health infrastructure. In addition, several questions concerning the epidemiology of HCV infection remain, and the answers to those questions could change or modify primary prevention activities. These questions primarily concern the magnitude of the risk attributable to sexual transmission of HCV and to illegal noninjecting-drug use.

Identification of the large numbers of persons in the United States with chronic HCV infection is resource-intensive. The most efficient means to achieve this identification is unknown, because the prevention effectiveness of various implementation strategies has not been evaluated. However, widespread programs to identify, counsel, and treat HCV-infected persons, combined with improvements in the efficacy of treatment, are expected to lower the morbidity and mortality from HCV-related chronic liver disease substantially. Monitoring the progress of these activities to determine their effectiveness in achieving a reduction in HCV-related chronic disease is important.