Clinical significance of bacteriologic screening in platelet concentrates

Despite routine bacterial screening with a bacterial culturing system (BacT/ALERT, bioMerieux) of platelet (PLT) concentrates, two cases of life-threatening sepsis attributed to transfused PLT products contaminated with Bacillus cereus were reported to the regional hemovigilance office in the southwest region of the Netherlands. These reports necessitated a retrospective evaluation of the currently applied bacteriologic screening program.

Bacteriologic screening of all PLT concentrates on production was introduced in October 2001. Aliquots (5-10 mL) of pooled PLT concentrates in additive solution were taken for cultures with the BacT/ALERT system 14 to 24 hours after donation. The total culturing period was 7 days and in case of positive signals, identification cultures were taken from the culture bottles. The results of the bacterial screening, identification, and clinical significance of possibly contaminated pooled PLT concentrates were evaluated retrospectively over a 2-year period.

In this period, a total of 28,104 pooled PLT concentrates were produced. Positive bacterial screening was found in 0.72 percent (n = 203). Of these, in 184 pooled PLT concentrates bacteria were cultured and identified, and in the remaining 19 (9.4%) identification cultures were negative. Before a positive screening was found, 113 PLT concentrates had already been transfused without the occurrence of clinical significant transfusion reactions.

Bacterial contamination of pooled PLT concentrates was not related to clinically significant transfusion reactions. Despite negative screening for bacterial contamination, life-threatening transfusion-transmitted infections by contaminated PLT products can still occur. Other strategies should be applied to guarantee a higher degree of bacteriologic safety.