Estimation of the infectious viral load required for transfusion-transmitted human T-lymphotropic virus type 1 infection (TT-HTLV-1) and of the effectiveness of leukocyte reduction in preventing TT-HTLV-1

Background and Objectives The risk of transfusion‐transmitted human T‐lymphotropic virus type 1 infection (TT‐HTLV‐1) after prestorage leucocyte reduction (LR) remains unknown, as the proviral load in the blood component that would cause TT‐HTLV‐1 is undetermined. On the basis of the distribution of HTLV‐1 proviral load among HTLV‐1‐sero‐positive blood donors, we attempted to estimate the proviral load for transfusion‐related infectivity. We also discuss the effectiveness of LR in preventing TT‐HTLV‐1. Materials and Methods The HTLV‐1 proviral load in 300 HTLV‐1‐sero‐positive blood donors was determined by real‐time polymerase chain reaction analysis. The proviral load required for transfusion‐related infectivity was estimated using historical TT‐HTLV‐1 frequency data from a retrospective study on patients who had received blood from HTLV‐1‐sero‐positive blood donors and the distribution pattern of HTLV‐1 proviral load among blood donors. Results HTLV‐1 proviral loads ranged between