Incidence and estimated rates of residual risk for HIV, hepatitis C, hepatitis B and human T-cell lymphotropic viruses in blood donors in Canada, 1990-2000.

Background: Since 1990, the Canadian Red Cross Society and Canadian Blood Services have been testing blood donors for hepatitis C virus (HCV) antibody and HCV nucleic acids and have supplemented HIV antibody testing with p24 antigen testing. We report trends in the incidence of blood-transmissible viral markers and estimates of the risk of undetected infection in donors over the last decade.

Methods: We extracted anonymous donor and blood-transmissible disease information from the Canadian Blood Services National Epidemiology Donor Database for 8.9 million donations from 2.1 million donors between June 1990 and December 2000. The risk of transfusion-transmitted infection (or "residual risk") refers to the chance that an infected donation escapes detection because of a laboratory test's window period (i.e., the time between infection and detection of the virus by that test). We determined the probability of residual contamination of a unit of blood after testing by using the incidence/window period model, which is based on the incidence of infection in repeat donors and the window period for each laboratory test. The viral markers evaluated in the study were HIV, HCV, hepatitis B virus (HBV) and human T-cell lymphotropic virus (HTLV).

Results: Except for HBV, the transmissible-disease rates of the other evaluated viruses decreased over the study period, with less of a decrease for HTLV. In 2000, the transmissible-disease-positive rate per 100 000 donations was 0.38 for HIV, 16.83 for HCV, 12.40 for HBV and 1.77 for HTLV. The residual risk of HIV, HCV and HTLV decreased over the study period; the residual risk of HBV fluctuated throughout the decade. The current residual risk per million donations is 0.10 for HIV, 0.35 for HCV, 13.88 for HBV and 0.95 for HTLV.

Interpretation: Except for HBV, the estimated risk of undetected infection (residual risk) has decreased over time. The rates of transmissible disease and the probability of undetected transmission of infection are at par with, if not lower than, those reported for other industrialized countries.