Fatal false‐negative transfusion infection involving a buffy coat platelet pool contaminated with biofilm‐positive Staphylococcus epidermidis : a case report

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. CASE REPORT 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. DISCUSSION 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. CONCLUSION 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.