Blood safety: bacterial screening of blood products

Screening of platelets for bacterial contamination at the Welsh Blood Service

BACKGROUND AND OBJECTIVE

This report details the results of the implementation of a bacterial screening system at the Welsh Blood Service and provides an estimate of the levels of bacterial contamination at the time of sampling.

MATERIALS AND METHODS

Apheresis (Caridian BCT) and buffy coat-derived pooled platelet components were sampled on day 1 for bacterial contamination and the sample was monitored throughout the lifespan of the platelet component. Unused platelet components were re-tested to determine the effectiveness of the screening. Results from the BacT/ALERT are uploaded to the in-house Blood Establishment Computer System (BECS) every 12 min. Positive alerts are automatically sent to staff, facilitating a timely intervention.

RESULTS

Between February 2003 and March 2010 the screening system tested 54 828 platelets and detected 257 (1 in 213) initial positives of which 35 (1 in 1567, 0·06%) were confirmed [95% confidence interval (CI), 0·04-0·08%]. Additionally, screening of 6438 unused platelet components detected another 6 (1 in 1073, 0·09%) confirmed positives not detected during initial testing (95% CI, 0·02-0·16%). Analysis of the data suggests that on day 1 the number of bacteria in such platelet component packs was between 5 and 62 cfus total. Day 1 culture has a sensitivity of 40%.

CONCLUSIONS

The bacterial screening system has removed a significant number, but not all bacterially contaminated platelet components from the supply. The sample volume is an important factor in sensitivity due to the low number of bacteria in a platelet component pack on day 1. An effective notification and recall system is a critical part of the bacterial screening system.