Bacterial contamination in platelets: incremental improvements drive down but do not eliminate risk

Area of Science:

• Transfusion Medicine
• Microbiology
• Infectious Disease Risk Management

Background:

• Bacterial contamination of platelet components (PCs) poses a significant transfusion-associated infectious risk.
• Canadian Blood Services (CBS) implemented bacterial testing of PCs in 2004 using the BacT/ALERT 3D system.
• Continuous monitoring of culture rates provides data on true/false positives and negatives.

Purpose of the Study:

• To compare bacterial contamination rates across different platelet (PLT) preparation methods.
• To evaluate the impact of protocol changes on bacterial detection and contamination rates.
• To assess the effectiveness of bacterial testing in reducing transfusion-associated infectious risk.

Main Methods:

• Analysis of national data from 12 CBS sites (March 2004 - October 2010).
• Comparison of bacterial contamination rates for apheresis, buffy coat, and PLT-rich plasma preparation methods.
• Evaluation of data before and after protocol changes, including sample testing volumes and skin disinfection methods.

Main Results:

• Initial positive rates varied significantly by PLT preparation method, with apheresis PCs highest.
• Confirmed positive rates did not differ significantly across preparation methods (p = 0.668).
• Increased sample testing volume (8-10 mL) raised initial positives and approached significance for confirmed positives (p = 0.055).
• Skin disinfection protocol changes did not significantly alter confirmed positive rates.
• Eight false-negative cases were reported, five linked to adverse transfusion reactions.

Conclusions:

• Bacterial testing and improved protocols incrementally reduce the risk of transfusing bacterially contaminated PLT concentrates.
• The occurrence of false-negative results indicates that the risk of bacterial contamination has not been entirely eliminated.
• Continued vigilance and refinement of testing protocols are necessary to further minimize transfusion-associated infectious risks.