More than 3,000 Canadians who received organ transplants during the past 20 years are being notified that there is a "theoretical" possibility they may have been infected with hepatitis or HIV from an immunosuppressive drug produced and used mainly in Toronto.

The drug -- called Rabbit Anti-Thymocyte Serum -- was developed at the University Health Network facilities in Toronto in the 1970s, and was produced by injecting an extract of human tissue into rabbits and extracting an anti-rejection serum from the rabbit's blood. The human tissue was never tested or screened for HIV or hepatitis.

"We're not aware of a single case where there has been an infection transmitted," said Dr. Alan Goldbloom, executive vice-president and chief operating officer at the Hospital for Sick Children in Toronto. "We are talking about a theoretical risk. When you ask the experts they say it is extremely remote, but we can not say it is zero.

Use of the serum is linked to some of Canada's largest hospitals, including Toronto General Hospital, as well as health facilities performing transplant surgeries in Ottawa, Hamilton, London and Kingston, Ontario, as well as one hospital in Quebec.

Letters are being sent to patients recommending they be tested for human immunodeficiency virus (HIV 1 and 2), hepatitis B virus (HBV), hepatitis C virus (HCV), and human T-cell lymphotropic virus (HTLV) at the time of their next regular appointment.

Rabbit anti-thymocyte serum is still in use, but the serums produced in hospital and university laboratories in the 1970s and 1980s have been replaced by a new commercial version, Thymoglobulin, that goes through two pasteurizations and cannot contain human viruses, according to a spokesperson for SangStat, the drug's manufacturer.

Other sources: National Post, Ottawa Citizen