Atypical bacterial growth within units of platelets challenges transfusion medicine dogma

Although transfusion-transmitted bacterial infection is relatively rare, mitigation of bacterial contamination of platelet units is arguably the top current transfusion-related safety concern. Several different technologies have been employed to detect or neutralize bacteria in platelet concentrates. However, studies of the efficacy of these systems have been hampered by problematic definitions of what represents a “true-positive” versus a “false-positive” culture result. In the current issue of the Journal of Clinical Microbiology (M. Cloutier, M.-È. Nolin, H. Daoud, A. Jacques, M. J. de Grandmont, É Ducas, G. Delage, and L. Thibault, J Clin Microbiol 56:e01105-18, 2018, https://doi.org/10.1128/JCM.01105-18), it was demonstrated that the growth of Bordetella holmesii is inhibited by the platelet storage environment, which may explain why the results of initial positive platelet cultures are not always confirmed by subsequent cultures later during the storage period. This important finding is at odds with the generally held belief within the field of transfusion medicine that initially positive platelet cultures that are not confirmed on repeat testing are instrumentation-based false positives. The clinical risk profile of organisms demonstrating storage-related low viability is worthy of further study.