Transfusion risk reduction: Testing for bacteria

Bacterial transmission by transfusion remains a significant problem in transfusion medicine and several Blood Services have introduced bacterial testing of platelet components. Platelet components present the greatest risk due to their storage at 18–22°C, which enhances the proliferation of most bacterial species. Platelet components were involved in 87% of bacterial fatalities in the USA between 2005 to 2009 and in 83% of bacterial transmissions in the UK between 1996 and 2011. The major challenge for testing is that (unlike viruses) bacteria may multiply in blood components. Key testing issues are when to test, what volume to test and which assay or assays to use? An ideal screening test needs to be rapid (2 h), sensitive (approximately 1 cfu/ml), specific, inexpensive and simple to use. No current tests fit these criteria. Culture assays are the most widely used for the detection of bacteria. BacT/ALERT™ is the most commonly used system world wide and can be regarded as the gold standard in this field. The sensitivity of culture is 1–10 cfu/ml and detection times are generally 18‐24 h. Rapid tests currently available include the Bacti‐Flow™ (sensitivity 10 2 cfu/ml) flow cytometric assay; the Verax (sensitivity 10 3 –10 5 cfu/ml) and BacTx™ (sensitivity 10 3 –10 4 cfu/ml) assays which detect bacterial cell wall antigens and the pH SAFE™ which detects pH change. In house molecular assays (sensitivity <50 cfu/ml) have been developed, but none are commercially available. Bacterial screen testing of blood components is a complex topic, but its implementation has undoubtedly increased the safety of the blood supply. In the USA, bacterial culture methods reduced the number of adverse bacterial transmissions by 50–75%, and in England no transmissions have been reported since implementation of routine culture in February 2011.