- Transfusion-associated septic reactions occurring during or following the transfusion of cellular blood components was one of the earliest recognised complications of allogeneic blood transfusions. The presence of bacteria in cellular blood products thus has been a problem for many decades and currently it is the most common microbiological cause of transfusion-associated morbidity and mortality. Transfusion-associated septic reactions due to contaminated platelet concentrates appear to be much more common than those due to red cell concentrates. The prevalence of contaminated cellular blood products (red cells and platelets) is approximately 1 in 2,000. However, the transfusion to a recipient of a contaminated blood product may not be associated with morbidity, because many contaminated blood product units contain only few bacteria and such transfusions may be innocuous to the recipient. In other instances, contaminated blood product units may contain large numbers of virulent bacteria and endotoxins, and their transfusion may be associated with significant morbidity and may even be lethal to the recipient. The prevalence of severe episodes of transfusion-associated sepsis has not been clearly established, but is probably of the order of 1 in 50,000 for platelet units and 1 in 500,000 for red blood cell units transfused. As a result of the increased recognition that such transfusion-associated septic episodes can occur, a variety of measures have been proposed to try to prevent and/or control the rate of contamination of blood products.