Background and Objectives
We introduced 100% screening of platelets for bacterial
contamination in 2005 to reduce the risk of clinical sepsis from platelet transfusion.
We test all outdating units again at expiry to assess the sensitivity of the initial test.
Materials and Methods
We test all platelet concentrates prior to release for clinical use
using a large volume automated culture technique on the day after manufacture. All units
that expire unused are retested. Platelets still in stock on day 4 of storage may have a
repeat culture performed, and are returned to stock with two extra days of shelf life.
Results
Of 43 230 platelet units screened, 35 (0·08%) were positive; of 8282 expired
unused, 18 (0·22%) were positive; and of 3310 day-4 retests, four (0.12%) were positive.
Overall sensitivity of the initial screening test was 29·2% (95% confidence interval
19·4 to 39·1%). Thirteen of the 35 positive screening tests would have been expected
to grow in both aerobic and anaerobic bottles; eight grew in aerobic culture only and
five grew in anaerobic culture only, indicating that the likely number of bacteria in the
contaminated platelet units at the time of sampling was less than 60 colony-forming
unit per platelet unit.
Conclusions
Screening platelet concentrates for bacterial contamination using the
most sensitive method available has a sensitivity of less than 40% because of the low
numbers of bacteria in the initial contamination. Effective resolution of this problem
will require a pathogen-inactivation technique.