Contents lists available at ScienceDirect Transfusion and Apheresis Science journal homepage: www.elsevier.com/locate/transci Reflections on the dynamics of bacterial and viral contamination of blood components and the levels of efficacy for pathogen inactivation processes Aicha Bah a , Marcia Cardoso a , Jerard Seghatchian b, ⁎ , Raymond P. Goodrich c, ⁎ a Terumo BCT Europe N.V., Zaventem, Belgium b International Consultancy in Blood Components Quality/Safety Improvement and DDR Strategies, London, UK c Colorado State University, Fort Collins, CO, USA ARTICLE INFO Keywords: Pathogen reduction Efficacy Contamination levels ABSTRACT 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 mea- sures. 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. 1. Introduction With the continual upgrading of donor screening and addition of multiple layers of screening tests, blood transfusion has become in- creasingly safer during the past decades. However, numerous infectious hazards from known and emerging pathogens still remain a matter of concern and can sometimes lead to fatal consequences in recipients of blood transfusion [1]. Continuous improvement in and implementation of blood safety measures can eliminate, or at least reduce, the risk of acquiring transfusion- transmitted infections. Pathogen reduction technologies (PRTs) have therefore been developed with the objective of inactivating pathogens, reducing the pathogen load and, by exten- sion, the risk of transmitting infections to recipients [2]. The ability of different PRT methods to reduce pathogen load and the risk of trans- fusion-transmitted infections (TTIs) has been the subject of multiple discussions over time [3]. Comparisons of “log reduction” or “log kill” among the Mirasol® Pathogen Reduction Technology (PRT) System (Terumo BCT), the INTERCEPT Blood System (Cerus), and the Thera- flex Platform (Macopharma) are commonly used to determine the most effective device for a given pathogen or group of pathogens. Analyzing the levels of PRT inactivation that are reported, however, requires understanding two concepts: first, the measurements of pathogen load in blood products; and second, the dynamics, infectivity, and disease transmission of various pathogens via transfusion of blood products. This manuscript is intended to evaluate the measurements used to quantify bacterial and viral titers in blood products, to provide a global view of the dynamics of bacteria and viruses that can be transmitted through blood product transfusion, and, lastly, to discuss and define adequate levels of pathogen inactivation needed to reduce the risk of TTIs. https://doi.org/10.1016/j.transci.2018.09.004 ⁎ Corresponding authors. E-mail addresses: jseghatcian@btopenworld.com (J. Seghatchian), ray.goodrich@colostate.edu (R.P. Goodrich). Transfusion and Apheresis Science xxx (xxxx) xxx–xxx 1473-0502/ © 2018 Elsevier Ltd. All rights reserved. Please cite this article as: Bah, A., Transfusion and Apheresis Science, https://doi.org/10.1016/j.transci.2018.09.004