Background: The risk of transfusion transmitted viral infection is now so low that mathematical modelling is required to estimate the residual risk. The first national viral risk estimates for hepatitis B virus (HBV), human immunodeficiency virus (HIV) and hepatitis C virus (HCV) were recently published by the Australian Red Cross Blood Service. Using several refinements to the original methodology, as well as an additional 2 years of data, new risk estimates have been derived.
Methods: Viral screening data for Australian donors for 2000/2003 were retrospectively analysed. The data were applied to three published models to estimate the residual risk of transmitting HIV, HBV, HCV or human T lymphotrophic virus (HTLV) by blood transfusion in Australia.
Results: Applying the three models to HBV, HIV and HCV, three point estimates of the residual risk per unit were calculated for each virus. The median point estimates were 1 in 1 339 000 for HBV, 1 in 1 in 7 299 000 for HIV, and 1 in 3 636 000 for HCV. Although the HTLV risk could not be equivalently calculated because of the lack of incident infection it was estimated to be considerably less than 1 in 1 000 000 using a separate method.
Conclusions: The most current and accurate estimate of residual risk of viral transmission in Australia has been provided in the present study. The residual risk in Australia is exceptionally small, continuing to decrease and is generally less than European or US risk estimates. These new estimates demonstrate that for viral transmission the Australian blood supply is amongst the safest in the world, and provide a basis for evaluating the cost benefit of future viral testing methodologies. (Intern Med J 2005; 35: 592–598)