Reducing the risk of transfusion-transmitted rickettsial disease by WBC filtration, using Orientia tsutsugamushiin a model system

BACKGROUND: Careful donor screening and infectious disease marker testing have significantly reduced the incidence of transfusion-transmitted diseases and improved the safety of the blood supply. However, transfusion-transmitted diseases resulting from the use of asymptomatic yet infectious donors continue to put patients at risk. This study was undertaken to determine if third-generation WBC filters could remove Orientia tsutsugamushi-infected cells from contaminated blood. STUDY DESIGN AND METHODS: Packed RBCs were inoculated with human MNCs infected with O. tsutsugamushi at levels estimated to occur in asymptomatic infectious donors. WBC reduction was accomplished with a third-generation WBC filter. Prefiltration and postfiltration specimens were collected, serially diluted, and injected into mice to determine the infectivity of the samples. RESULTS: Mice receiving WBC-reduced packed RBCs showed no signs of illness or markers of infectivity, which suggested that a reduction of as much as 10(5) infectious rickettsiae could be achieved by filtration. CONCLUSION: The high-efficiency, third-generation, WBC-reduction filters that were tested may provide protection against the transfusion transmission of scrub typhus rickettsiae by removing from contaminated blood cells that contain intracellular bacteria.