title: Fatal false-negative transfusion infection involving a buffy coat platelet pool contaminated with biofilm-positive Staphylococcus epidermidis: a case report.
abstract: BACKGROUND
  Bacterial contamination of platelet concentrates (PCs) poses the major posttransfusion infectious risk in developed countries. The aerobic microorganism most frequently isolated from PCs is coagulase-negative Staphylococcus epidermidis, a normal inhabitant of the human skin, which has been involved in fatal transfusion reactions worldwide.
  
  
  METHODS
  In September 2014, a splenectomized elderly male patient, suffering from leukemia, was transfused with two 5-day-old buffy coat platelet (PLT) pools. The patient returned to emergency on the same day with a low-grade fever. He was bacteremic and died on the next day. Microbiology and molecular testing of a blood sample from the patient and one of the PCs yielded the same S. epidermidis strain. Further analysis demonstrated that this S. epidermidis isolate displays a biofilm-positive phenotype in PCs.
  
  
  CONCLUSIONS
  At Canadian Blood Services, PCs are screened for bacterial contamination with the BacT/ALERT system (bioMérieux) at approximately 24 hours postcollection. The implicated PC had been tested and yielded a false-negative culture result. A titration experiment indicated that, at the time of screening, the contaminated PC had a titer of less than 0.74 colony-forming units (CFU)/mL (<227 CFUs/unit) of S. epidermidis. Mathematical models have predicted that up to 70% of PCs contaminated with coagulase-negative staphylococci at concentrations of 0.02 CFU/mL can be missed by BacT/ALERT screening.
  
  
  CONCLUSIONS
  Despite several mitigation strategies, false-negative cultures with current PLT screening practices still occur. This report creates awareness of the pathogenicity of opportunistic S. epidermidis, a low-virulence organism, in susceptible patients who may not develop a typical transfusion reaction.
authors.affiliation: Canadian Blood Services.
authors.forename: Yuntong
authors.initials: Y
authors.lastname: Kou
authors.affiliation: Health Canada, Ottawa, Ontario, Canada.
authors.forename: Franco
authors.initials: F
authors.lastname: Pagotto
authors.affiliation: Canadian Blood Services.
authors.forename: Barbara
authors.initials: B
authors.lastname: Hannach
authors.affiliation: Canadian Blood Services.
authors.forename: Sandra
authors.initials: S
authors.lastname: Ramirez-Arcos
mesh_terms: D000369:Aged, 80 and over; D018441:Biofilms; D058621:Blood Buffy Coat; D017809:Fatal Outcome; D006801:Humans; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000628:therapy*; D008297:Male; D017713:Platelet Transfusion; D013203:Staphylococcal Infections / Q000635:transmission*; D013212:Staphylococcus epidermidis / Q000502:physiology*