T o prevent the spread of hepatitis C virus (HCV), prevention and counseling measures should be appropriate to the presence and magnitude of risk. Assessing risk is based on the epidemiologic characteristics of HCV, including modes of transmission, which persons are at increased risk or have a high prevalence of infection, and the amount of disease or infection attributable to the risk. In 1998, the Centers for Disease Control and Prevention (CDC) convened a meeting of expert consultants to review the available data and develop recommendations for the prevention and control of HCV infection. These recommendations were published in October 1998. 1 This review summarizes highlights of the epidemiologic data used to support these recommendations and includes data that have become available since that publication.
Risk Factors Associated With Acquiring HCV InfectionThe most reliable data on risk factors associated with acquiring infection are obtained from cohort (prospective) studies and case control (retrospective) studies of acute disease. 2 In cohort studies of HCV infection, the presence of exposure (e.g., blood transfusion) was determined in a defined population (e.g., hospitalized patients), and the population was followed to compare the incidence of infection and disease in the exposed group compared with the incidence in the nonexposed group. In case control studies of acute hepatitis C, the population sample was selected based on the presence or absence of newly acquired, symptomatic disease, and the proportions of cases with histories of various exposures (e.g., blood transfusion, injection drug use, number of sex partners) during the 6 months before onset of disease were compared with those of the controls. For these studies, cases were identified from among persons seeking medical care for acute viral hepatitis in public and private outpatient and inpatient settings and the controls were selected