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.

Recovery and viability of Orientia tsutsugamushi from packed red cells and the danger of acquiring scrub typhus from blood transfusion.

BACKGROUND: The purpose of this study was to determine whether infective Orientia tsutsugamushi, the etiologic agent of scrub typhus, could survive normal blood banking processing and storage procedures. STUDY DESIGN AND METHODS: Mononuclear cells isolated from whole blood by density gradient centrifugation were inoculated with O. tsutsugamushi, Karp strain. Infection of the mononuclear cells was confirmed by Giemsa stain, direct fluorescent antibody assay, and polymerase chain reaction using primers specific for the groESL operon of O. tsutsugamushi. The quantity of rickettsial particles in each preparation was determined by direct counts from the Giemsa-stained preparations. Infected mononuclear cells were returned to their respective aliquots of packed red blood cells, which were then either stored at 4 degrees C or glycerolized and frozen at -70 degrees C. RESULTS: Rickettsiae survived up to 10 days (but not 30 days) of refrigerated storage and 45 days of frozen storage, as determined by inoculation of mice with 0.5-mL aliquots of the blood components. Infection of the mice was determined by illness, death, direct fluorescent antibody assay of peritoneal smears, polymerase chain reaction of blood, and enzyme-linked immunosorbent assay detection of antibodies in plasma. CONCLUSION: Because the quantity of rickettsiae injected into the mice was comparable to the quantity reported in the literature for human blood during natural infections, scrub typhus could present a risk in blood collected from donors in endemic areas. This may especially be true, because people can be rickettsemic before illness, after successful antibiotic treatment, and chronically after resolution of disease.