Current status of bacterial detection in blood components – successes and challenges
Authors: Schmidt M. , Seifried E. 
Published: June 2012

Background  Blood safety and the prevention of transfusion‐transmitted pathogens are among the principal aims of transfusion medicine. Based on the many improvements over the last decade in donor selection programs, the implementation of nucleic acid testing (NAT) and the introduction of third‐ and fourth‐generation serology assays into blood donor screening, the residual risk of transfusion‐transmitted viruses has been reduced to a minimum, and the quality and safety of blood components are at their highest level ever. In contrast, the residual risk of bacterial transmissions, especially in platelet concentrates, is an on‐going challenge in transfusion medicine. To improve blood safety regarding bacterial contaminations, many countries have implemented bacterial culture methods, in combination with the negative‐to‐date concept. This strategy has improved blood safety and reduced transfusion‐transmitted fatalities due to bacterial infections. Nevertheless, false‐negative screening results have been reported in some cases. The current manuscript summarises the clinical and experimental data based on culture methods and rapid bacterial detection systems.

Methods  Many countries have implemented bacterial culture methods (BacT/ALERT, BACTEC or PAL eBDS), in combination with the negative‐to‐date concept. Differences between countries have been recognised regarding testing with aerobic bottles alone or with aerobic and anaerobic bottles and regarding sample input volumes. Therefore, international comparisons for the prevalence and incidence of contamination rates are different between countries. Within the last few years, a couple of rapid bacterial detection methods have been developed in experimental spiking studies. The most promising methods are FACS systems, such as Bactiflow, impedance measurements, pan generic detection, and automated generic 16s nucleic amplification testing (NAT).

Results  Culture methods, in combination with the negative‐to‐date concept, have been implemented in many countries as a ‘gold standard’ to improve blood safety. Analytical sensitivity could be increased by using aerobic and anaerobic bottles, as well as by using an input volume of 8–10 ml per bottle. Countries using both screening bottle types have detected Probionibacterium acnes in the majority of cases. False‐negative screening results with fatal outcomes have been prevented. In contrast, rapid bacterial detection methods have been investigated in spiking studies. Clinical data are available in Germany for Bactiflow and 16s NAT. The analytical sensitivity of rapid bacterial detection methods is 1–2 log phases less than for culture methods.

Conclusions  In addition to diversion of the first 30–40 ml, reduction of platelet shelf life and the implementation of pathogen‐reduction methods, blood donor screening for bacterial contamination in platelets has been able to improve blood safety and to prevent fatal septic reactions. Different rapid bacterial detection methods are currently feasible for routine screening and to enable new opportunities. The negative‐to‐date concept, with the residual risk of sampling errors, might be replaced by the rapid release of untested platelets on day 1 and day 2 after donation, in combination with a late sampling‐screening model on day 3 after donation with rapid bacterial detection systems. Clinical data for the newly developed rapid detection methods are eagerly awaited.