Strategies of bacteria screening in cellular blood components.

Since the impressive reduction of transfusion-transmitted virus infections, bacterial infections by blood transfusion represent the most important infection risk. Platelet concentrates are the current focus of attention, as they are stored under temperature conditions which allow growth of contaminating bacteria up to 10(10) and more microbes per platelet bag. This paper does not consider the pathogen reduction methods but will assess suitable screening methods. Beside conventional microbiological approaches or surrogate markers, several efficient methods able to detect bacterial contamination in platelets are available on the market. They need to be divided into two different methodological principles: the cultivation methods and rapid methods. Cultivation or incubation methods require some time for signal production as they depend on growth of microbes. Thus, they have to be combined with early sampling, i.e., the sample to be examined has to be drawn from the blood component 1 day after donation. Their advantage is the relatively uncomplicated implementation into the logistics of blood banks. Because of the initially very low count of bacteria after donation, a certain small sampling error in application of that strategy remains. Rapid methods are able to produce the diagnosis within a short time. Therefore, they allow postponing of sample drawing, ideally up to the time immediately before transfusion. However, this procedure causes logistic complications. On the other hand, late sampling combined with a rapid method will prevent the transfusion of highly contaminated platelet concentrates leading to acute septic shock up to the death of the patient. Considering the sum of different aspects including the supply of patients, the potential improvement of microbial safety of platelet concentrates is comparable in both strategies.