Relationship between bacterial load, species virulence, and transfusion reaction with transfusion of bacterially contaminated platelets

Background. Bacterial contamination is currently the major infectious hazard of platelet transfusion, but associations between bacterial species and quantity and transfusion reactions have not been characterized. Methods. Patients receiving platelets from July 1991 through December 2006 were observed using active surveillance by quantitative culture of platelets at the time of issue or passive surveillance by investigation of clinical reactions in patients and culture of implicated units. Patient reactions were classified by type and severity and were correlated with bacterial species and number. Endotoxin content of gram-negative contaminants was determined by limulus lysate assay. Results. Fifty-two bacterially contaminated platelet units were detected (50 by active and 2 by passive surveillance). Rates of bacterial contamination and septic transfusion reactions were 32.0-fold and 10.6-fold higher, respectively, as determined by active versus passive surveillance (P<.001). Including 2 index cases, bacterial contaminants included gram-negative bacilli in 4 units (3 of which were associated with fatal reactions), staphylococci in 44 units, streptococci in 4 units, and Bacillus cereus in 2 units. Endotoxin content of the 4 units that were contaminated with gram-negative bacilli ranged from 11,373 to 173,130 endotoxin units. Reaction severity was greater for units with bacterial counts of >= 10(5) colony-forming units/mL and higher bacterial virulence. A detection method with a 10(3) colony-forming units/mL threshold would detect 190% of contaminants. Conclusions. Active surveillance detected 32-fold more bacterially contaminated platelet units and 10.6-fold more septic reactions than did passive surveillance, and virulent species and bacterial counts of >= 10(5) colony-forming units/mL were associated with more-severe transfusion reactions. Improved detection methods or use of pathogen inactivation technology are needed to eliminate this problem.