Bacterial safety of blood products

Project leader: Dirk de Korte PhD

Contamination of platelets with bacteria is a major microbiological risk in blood transfusion. This applies especially to platelet concentrates (PCs) because their storage conditions, at room temperature and under constant agitation, support bacterial growth. Therefore both the prevention of contamination and gathering knowledge on the type of contamination are the subject of research within the blood bank. 2011 marked 10 years since screening of PCs was started in the Netherlands.

10 years of screening for bacterial contamination of platelet concentrates in the Netherlands
As contamination of platelets with bacteria is a major microbiological risk in blood transfusion, screening for bacterial contamination can reduce the frequency of bacterial transmission considerably. Since 2001, all PCs produced in the Netherlands are cultured with the BacT/Alert culturing system with large volume (7.5 ml) cultures in both an aerobic and anaerobic bottle. About 63,000 pooled buffy coat derived PCs are produced per year and about 4000 aphaeresis PCs are collected. PCs are released on a ‘negative to date’ basis. When a PC from pooled buffy coats is flagged positive for bacterial growth, the 5 related red blood cell (RBC) concentrates are also cultured for bacterial growth. Due to the short shelf life it was decided to perform no retesting on PCs, but to destroy the product. However, RBCs are released again if negative during the 7-days culture.

Due to the principle of ‘negative to date’, PCs which are already transfused can have a positive culture result afterwards. If this is the case, the hospital is contacted and it is explained that there is a chance that the transfused unit was bacterially contaminated. It is also explained that the growth in the culture is normally ahead of the growth in the PC from which the sample was taken and that a bacterial transmission by the PC would be rare. This message was very well understood and accepted by the clinicians. During the years in which 100% screening was applied, the number of units released as ‘negative to date’ with a positive culture after being transfused, decreased substantial by introduction of the deviation bag. In the initial years we had about 230 units a year being released as ‘negative to date’, but with a subsequent positive culture after transfusion. After introduction of the deviation bag this decreased to a mean of 110 per year. Over a period of 4 years (2006-2009) an active look-back was undertaken for 435 patient records of these transfusions and only three cases with a reported transfusion reaction were found. For these cases in which a transfusion reaction was reported the imputability of being related to the transfusion of a contaminated PC was unlikely.

The diversion of the first volume of collected blood was introduced by Sanquin in 2004. As a result the number of positive screening cultures decreased significantly from 0.85% to 0.37%. The number of transfusion-transmitted bacterial infections by PCs is currently less than 1 per 2 years in the Netherlands. There are no indications that ‘false negative’ cultures add a high risk to the transfusion of PCs (Scientific Report 2010). Looking back over 10 years of bacterial screening system for PCs, the conclusion was that the system as applied in Sanquin, in combination with diversion of the first collected blood, resulted in a safe system with respect to microbiological infection due to platelet transfusions. 

Key publications

Last edited on: 2 October 2012