Estimation of human T-lymphotropic virus incidence in blood donors from observed prevalence.

Repeat donors in Australia will shortly cease to be tested for human T-lymphotropic virus (HTLV), removing the ability to measure repeat donor incidence. A risk threshold for repeat donors was investigated based on previous modelling and a conservative ratio between prevalent and incident infections. It was estimated that 26 infections per 100 000 new-donor donations would be associated with an incidence in repeat donors approaching the tolerable risk threshold if sustained over several years. We propose to trigger formal risk assessment at this point, and believe this solution may be useful for other blood services that reduce their HTLV testing requirements.