Epidemiology. Hepatitis C virus (HCV), identified in 1988, is an RNA virus that appears to be responsible for most instances of parenterally transmitted non-A, non-B hepatitis. The virus seems to mutate frequently and appear in many subtypes. HCV is associated with transfusions of contaminated blood and blood products such as plasma, factor VIII, factor IX, fibrinogen, cryoprecipitate, and immune globulin. HCV is also transmitted by IV drug abuse, hemodialysis, and organ transplantation. It appears to be transmitted rarely by familial, sexual, or maternal-infant exposure. Heterosexual transmission seems to be much less frequent than homosexual transmission of the virus. Health-care workers exposed to a patient or the blood of a patient infected with HCV may acquire hepatitis C either from an accidental needle stick or without such an incident; however, the risk in such cases seems to be less than 10%. This occurrence has been documented in dialysis and oncology units and in plasmapheresis centers. Sporadic instances of hepatitis C occur and may account for 6% to 36% of the sporadic cases of hepatitis seen in urban areas. There may be unnoted percutaneous exposure among such patients. However, hepatitis C may also be transmitted by nonpercutaneous mechanisms. The epidemiology of hepatitis C has not been completely defined.