Reflections on the dynamics of bacterial and viral contamination of blood components and the levels of efficacy for pathogen inactivation processes

Blood transfusion safety has been increasingly improving during the past two decades. However, threats from both known and emerging pathogens require continual improvement and re-assessment of blood safety measures. In this respect, we are currently witnessing the broader implementation of Pathogen reduction technology (PRT) for blood complements. These methods, combined with existing safety measures, have helped to reduce the pathogen risks of transfusion-transmitted infections. Currently multiple reviews have compared levels of inactivation between different commercialized PRTs. However, to analyze levels of pathogen inactivation, it is necessary to understand the dynamics of infectivity as well as the modes of disease transmission by blood transfusion for various pathogens. It is well known that contributing variables include donor characteristics through the processing of blood components to ultimately the recipient characteristics, which create enormous variability in overall outcomes relative to disease transmission. The aim of this paper is to discuss bacterial and viral contamination of blood components in order to determine adequate levels of efficacy and subsequent disease transmission safety of current pathogen inactivation protocols that are designed to reduce the risk of transfusion-transmitted infections. In such a conceptual analysis, however, it is important to understand several contributing factors including the measurement of pathogen load in blood products and the dynamics, infectivity and disease transmission of various pathogens via transfusion of blood components and products. In many cases, the log reduction values observed do not truly reflect the extent of reduction in the levels of infectivity that are observed clinically. Results from clinical trials and hemovigilance programs upon routine implementation of PRT methods provide a more direct insight into effectiveness with regard to clinical relevance of in vitro spiking studies. These issues are briefly addressed in this manuscript.