Blood safety: bacterial screening of blood products

Abstract

Bacterial contamination of blood components can cause death and serious morbidity in transfusion recipients [1–3]. Numerous measures to prevent and detect bacterial contamination have been introduced to reduce this hazard. Detection methods, including screening of blood components, are the subject of this review. Preventive measures include careful donor selection and predonation health screening, with donor deferral and follow-up of postdonation information as required [4,5]; optimization of blood collection and manufacturing processes, including improvements in skin cleansing procedures [6–9], choice of collection method and consumables, diversion of initial volume away from the collection bag [10–16], environmental monitoring, and greater availability of the use of apheresis platelets to minimize exposure to donor skin flora [17,18]; developments in pathogen reduction technologies [19–24]; attention to component storage and handling; and promotion of evidence-based clinical transfusion practice [24,25]. However, in spite of the introduction of advancements such as these, haemovigilance programs internationally continue to report serious adverse events because of bacterial contamination. For example, in spite of an overall reduction in numbers of cases reported annually to the French national haemovigilance programme since 2000, there were nine clinical cases in 2008 with imputability ratings of ‘likely ⁄ possible’ to ‘certain’, including one death because of Escherichia coli contamination of a platelet transfusion [26]. In the same year, the annual report from the Serious Hazards of Transfusion (SHOT) scheme described six confirmed clinical cases of sepsis in the United Kingdom because of bacterial contamination of platelet units, with consequences ranging from minor morbidity to death [27]. The spectrum of bacterial contamination ranges from detection of bacteria on routine component surveillance testing without apparent consequence to fatal sepsis. Recognition of transfusion-related sepsis can be difficult at the bedside, especially where patients may be already febrile and ⁄ or on antibiotics for suspected sepsis from other sources [28,29]. In order for bacterial contamination events to be captured by haemovigilance systems, the cases must first be identified clinically, confirmed with appropriate investigations, and then reported at institutional and programme levels. Haemovigilance programs are at various stages of development in different regions. Where they do exist, in some jurisdictions participation is mandatory and in other cases voluntary and therefore not universal. Different systems require variable levels of clinical certainty and laboratory confirmation, and some cases which are deemed highly likely on clinical grounds are unable to be confirmed because of unavailability or inappropriate handling or storage of blood component or patient samples. Thus, the number of confirmed and reported transfusion-related clinical cases can be considered the ‘tip of the iceberg’ or perhaps ‘the nose of the crocodile’ – with the majority of bacterial contaminations of blood components hidden below the surface, and many associated with no apparent harm, but with the potential for devastating outcomes. The cases included in haemovigilance reports therefore represent only a subset of total bacterial events. Even the definition of what constitutes a case of transfusion-transmitted bacterial contamination is a matter of some discussion. SHOT [27] defines a confirmed transfusion-transmitted infection as a case where: • the recipient had evidence of infection post-transfusion, and there was no evidence of infection prior to transfusion, and no evidence of an alternative source of infection; • and either at least one component received by the infected recipient was donated by a donor who had evidence of the same transmissible infection • or at least one component received by the infected recipient was shown to contain the agent of infection. The Dutch Transfusion Reactions in Patients (TRIP) haemovigilance system has recently expanded its scope of reportable bacterial events [30]. To the previous category of ‘post-transfusion bacteraemia ⁄ sepsis’, defined as ‘clinical symptoms of bacteraemia ⁄ sepsis arising during, directly after or some time subsequent to a blood transfusion, for which there is a relevant, positive blood culture of the patient with or without a causal relation to the Correspondence: Erica Wood, Australian Red Cross Blood Service, PO Box 354, 3205 South Melbourne, Victoria, Australia E-mail: woodericam@hotmail.com ISBT Science Series (2010) 5, 46–51