Background: Testing for possible microorganism contamination in umbilical cord blood (UCB) is essential for validating the product safety of allogeneic cellular therapeutics. We analyzed the level of contamination and related factors at the largest public cord blood bank in Korea. In addition, we also studied the influence of cryopreservation on contaminating microorganisms.

Methods: UCB was collected, transported, processed, and stored according to standard operating procedures. Microbial detection and identification was performed using a conventional automated blood culture system (BacT/ALERT; bioMérieux, France) with an inoculum of 5-10 mL plasma for pre-freezing UCB. Forty randomly selected non-conforming units were thawed and studied for microbiologic recovery with an inoculum of 2.5 mL.

Results: Among a total of 21,236 UCB, 677 (3.19%) were positive for culture. The most frequently identified organism was Lactobacillus spp. (17.2%), followed by Bacteroides spp. (10.1%), coagulase negative staphylococcus (6.4%), except the unidentified gram- positive bacillus (21.4%). The contamination rate was higher in vaginal delivery specimens than in cesarean section specimens (4.1% vs. 0.7%, P＜0.001), and differed by collection center (0.7-25.4%, P＜0.001). Only 55% after-thaw cultures of non-conforming units were positive.

Conclusion: We determined the contamination rate of UCB in Korea in a large sample size. The results of this study could be used as baseline data at collection centers for quality control purposes. The low recovery rate of microorganisms after cryopreservation presents a possible way to rescue some non-conforming cord blood units, although further study is needed to confirm the reduction of microbiological burden. (Ann Clin Microbiol 2013;16:39-44)