An archived serum sample as a clue for identifying the primary source of a nosocomial hepatitis C virus outbreak in a haemodialysis unit.

Due to an unexpected technical error, patients at a dialysis unit who were seronegative for hepatitis C virus (HCV) were temporarily transferred to another dialysis unit next to a ward reserved for HCV-seropositive patients. In the following 7 months, 17 patients were diagnosed as anti-HCV positive. The aim of the study was to reveal the cause of this nosocomial infection. Anti-HCV-positive sera were further tested by molecular methods. Data collection and on-site epidemiologic inspections were carried out. The source of the nosocomial infection proved to be a seropositive patient treated at the unit, who died before the outbreak was recognized. The exact date of the infection was determined.