Managing discordant results for bacterial cultures between samples from plateletpheresis products at 24 hours and those from QA samples for sterility after 5-day storage

A hospital-based donor center in Southern California has implemented a bacterial detection QA system using the BacT/ALERT culture system for all plateletpheresis products collected at their facility. Products are sampled 24 hours after they are collected, and are cultured and observed for 5 days. When they train a new operator on any of their apheresis devices that collect platelets, they perform sterility testing of the first products collected by the new operator, according to the Guideline for the Collection of Platelets, Pheresis Prepared by Automated Methods, published by the FDA on October 7, 1988. According to the FDA document, the sample for culture is obtained from the product on day 5 and then is cultured according to a protocol described in 21 CFR 610.12. The inquiring colleague asks if anyone has received clearance from the FDA to use their bacterial detection culture QA results in place of the sterility testing of products as defined in 21 CFR 610.12, when a new equipment operator is trained? The reason this question is particularly interesting is that the inquiring colleague's institution has observed a discordant set of results when a negative BacT/ALERT was paired with a positive sterility test culture taken at day 5. In the discordant case, it appears that the sterility test culture was contaminated, but this kind of discordance obviously creates a real dilemma when a product is tested twice by different methods and conflicting results are observed. What has been the experience in the field and does anyone have a better way to approach this problem?

The following response has been received.

ADDENDA Mar. 19, 2004

1. A transfusion medicine physician from North Carolina reports that this e-Network Forum discussion actually raises two related interesting questions.
   • Will the FDA allow the use of a culture at 24 hours of storage in lieu of the day 5 culture as described according to the Guideline for the Collection of Platelets, Pheresis Prepared by Automated Methods, published by the FDA on October 7, 1988?
   • According to the FDA document, the sample for culture is obtained from the product on day 5 and then is cultured according to a protocol described in 21 CFR 610.12.  Are the two approved culture methods (BioMerieux and Pall) considered equivalent?

With regards to the first question, the North Carolinian physician thinks the answer is 'NO', as he had heard the FDA repeatedly state, it is not yet clear how predictive a 24 hour culture is of a day 5 culture. He adds that a large national study to address this question will tentatively be starting this year.  It is hoped that the data from this study will also be used to allow 7 day storage of platelets. Nevertheless, some prelimary pilot data is available to address this question:

• Brecher et al reported on a total of 2397 apheresis platelets were sampled on Day 2 of storage (collection day=Day 0) and issue (or following outdate, Days 6-8) and cultured with  an automated liquid culture system (BacT/ALERT 3D Microbial Detection System) for 7 days. There was one false-positive aerobic bottle and one false-positive anaerobic result due to inadvertent contamination of a bottle. Thus, the overall true-positive rate was 7 of 2397 apheresis units (0.29%) with a true-positive rate for aerobic organisms of 0.13% and an anaerobic true-positive rate of 0.17%. The false-positive rate was 2 out of 4794 samplings (0.04%) or 2 out of 9588 bottles (0.02%).  In no case did an issue (or outdate) detect contamination that was not detected by the Day 2 culture. (Brecher ME, Hay SN, Rothenberg SJ. Monitoring of apheresis platelet bacterial contamination with an automated liquid culture system: a university experience. Transfusion. 2003 Jul;43(7):974-8.)
• In contrast, Rock recently reported on the use a the Pall BDS in 12,062 individual RDPs.  Aliquots from PLT pools were positive in 80 of 2201 pools (i.e. at time of issue) when tested by manual (plate) methods. Of these, 79 (3.6%) were false-positives and 1 unit contained coagulase-negative Staphylococcus. This underscores the high false positive rate that can be seen with manual plate cultures and the importance of excellent aseptic technique. (Rock G, Neurath D, Toye B, Sutton D, Giulivi A, Bormanis J, Olberg B, Holme S, Wenz B, Ortolano G, Nelson E.The use of a bacteria detection system to evaluate bacterial contamination in PLT concentrates.Transfusion. 2004 Mar;44(3):337-42.)

With regards to the second question, the North Carolinian says that according to the FDA document, the sample for culture is obtained from the product on day 5 and then is cultured according to a protocol described in 21 CFR 610.12.  Since the two quality control culture methods were approved as 510K submissions, in the eyes of the FDA, these methods should be equivalent.  Specifically, the BioMerieux was compared to the method described in 21 CFR 610.12 (i.e. thiogycollate broth), and the Pall BDS was compared to agar plate cultures.

See:

• Brecher ME, Means N, Jere CS, Heath D, Rothenberg S, Stutzman LC. Evaluation of an automated culture system for detecting bacterial contamination of platelets: an analysis with 15 contaminating organisms. Transfusion. 2001 Apr;41(4):477-82.
• McDonald CP, Rogers A, Cox M, Smith R, Roy A, Robbins S, Hartley S, Barbara JA, Rothenberg S, Stutzman L, Widders G.  Evaluation of the 3D BacT/ALERT automated culture system for the detection of microbial contamination of platelet concentrates. Transfus Med. 2002 Oct;12(5):303-9.
• Ortolano GA, Freundlich LF, Holme S, Russell RL, Cortus MA, Wilkins K, Nomura H, Chong C, Carmen R, Capetandes A, Wenz B. Detection of bacteria in WBC-reduced PLT concentrates using percent oxygen as a marker for bacteria growth. Transfusion. 2003 Sep;43(9):1276-85.

He concludes saying: "In point of fact, many centers have been using automated cultures for many years in lieu of thioglycollate cultures and I am not aware of anyone being cited for this practice.  FDA of course, has the final say in these matters."

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