Hepatitis C virus (HCV) causes liver inflammation. The virus is most commonly transmitted when a person comes in close contact with infected blood, usually by being stuck with a needle, as in injection drug use, body piercing, or tattooing. Outbreaks of HCV infection are unusual, especially in health care settings. In 2002, officials in Nebraska learned of a possible HCV outbreak involving 4 patients. The only common factor among these patients was treatment at the same cancer clinic. The officials suspected that the patients somehow became infected from the treatment they received in the clinic.