Objective: To re-examine the 1992 decision by Australian Red Cross for its blood banks to screen blood donors for antibody to human T-cell lymphotropic virus type I (HTLV-I) by determining the risk of its transmission by blood transfusion.
Methods: Data on patterns of return behaviour by repeat blood donors in Victoria were modelled to deduce the number of donors giving repeat donations in Australia from March 1993 to December 1995. Data on annual donor and issued cellular blood products from 1992 to 1995 were obtained from national Red Cross statistics. From the numbers of donations given by repeat donors, together with the number of new donors, the number tested for HTLV-I was deduced. The number and characteristics of donors screened positive for HTLV-I antibody were collated. The crude prevalence of HTLV-I was calculated by dividing the number of donors with HTLV-I by the total number of donors (repeat donors and new donors). The incidence of HTLV-I was calculated by dividing the number of seroconversions in repeat donors by the cumulative period of donor exposure.
Results: Sixteen homologous and five autologous donors were found to be positive for HTLV-I; none seroconverted and no clear risk factors for HTLV-I were identified. The prevalence of HTLV-I in Australian donors is 1 in 100,000 and the incidence less than 1 in 1 million person-years. In the absence of HTLV-I screening, the calculated risk of a transfused patient developing HTLV-I infection is 1 in 370,000, with a risk of developing HTLV-I disease of 1 in 9 to 15 million.
Conclusion: Three possible future courses of action for screening for HTLV-I are to screen every donation, to screen only new donors or to discontinue screening altogether. Using the information in this study, public discussion should be encouraged to assist stakeholders to agree on an acceptable level of risk and an appropriate level of screening for HTLV-I in Australia.