The three factors that directly influence the incidence of hepatitis associated with blood transfusion are the (1) carrier rate in the donor, (2) the titer of the infectious agent in the carrier, and (3) the susceptibility of the recipient. Australia antigen provides a device for identifying the carriers and the proportion of healthy persons found to be positive, which varies widely from country to country1 and even between different socioeconomic groups within the same country.2
It may be assumed for practical purposes that any unit of blood in which Australia antigen has been detected contains a considerable amount of the infectious agent. It has been shown in volunteer experiments that a 0.01 ml of icterogenic serum is as effective in causing infection as 200 times this amount.3 Direct titration of another batch of icterogenic serum gave an end point of 106 50% tissue culture interfering dose