The Weusten infectivity models do not give 95% confidence bounds for the risk estimates because—in addition to the considerable uncertainty and variability of ID50 values in stored blood components—other input parameters also have wide confidence limits, including transfusion plasma volume, the 95% and 50% LODs of the NAT method, the uncertainty in standardization of HBV-DNA genome copies or virion numbers, the viral doubling time in the acute phase, and the viral load distribution of different HBV genotypes in the later anti-HBc-positive infection stages. The gene discussed is BRD2; the disease is infection.