The greatest variation in prevalence of HCV infection occurs among persons with different risk factors for infection. The highest prevalence of infection is found among those with large or repeated direct percutaneous exposures to blood (e.g., persons with hemophilia treated with clotting factor concentrates produced before 1987, injecting-drug users, and recipients of transfusions from HCV-positive donors). Moderate prevalence is found among those with frequent but smaller direct percutaneous exposures (e.g., long-term hemodialysis patients). Lower prevalence of HCV-infection is found among those with inapparent percutaneous or mucosal exposures (e.g., health-care workers). Lowest prevalence of  HCV infection is found among those with no high-risk characteristics (e.g., volunteer blood donors). The estimated prevalence of persons with different risk factors and characteristics also varies widely in the United States population (Table 1).