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Abstract
Collection and processing of cord blood (CB) for transplantation is associated with significant risk of microbial contamination, hence standards mandate microbial screening of the final product. However, factors affecting contamination, the survival of microorganisms in CB and the sensitivity of current screening methods to evaluate microbes in the small volume tested are poorly understood.
CB was collected and processed using standard closed system techniques. Data from over 13,000 CB was analysed to determine factors affecting microbial contamination. Stored CB with known microbial contamination were thawed and re-screened. Additional fresh CB was spiked with microbial organisms (at 1-10 CFU/mL). Samples were screened using the BacT/Alert (Biomérieux) and/or and BACTEC (Becton Dickinson) systems using various combinations of culture bottles (adult aerobic/adult anaerobic/paediatric), sample volumes (1-10mL) and sample types (plasma discard, RBC discard or final product).
Of 13,344 CB screened over a 14-year period, 4.0% tested positive for contamination, with Bacteroides sp., Staphylococcus sp., and Propionibacterium sp. the most common isolates. Multivariate analysis demonstrated independent variables associated with higher contamination rates were vaginal delivery, collection by obstetric staff and use of an anaerobic culture bottle.
Contaminants were detected post-thaw in 63% of stored contaminated CB and 85% of spiked CB. Twenty percent of spiked organisms were not detected in pre-freeze samples but were detected post-thaw. Post-thaw organism detection in spiked CB was higher in adult bottles (80%) than paediatric bottles (61%). Inoculating final product into a paediatric bottle only detected 15% of obligate anaerobes whereas a combined fraction inoculation showed superior detection (70%). Similar detection rates were observed for the BacT/Alert and BACTEC systems.
This study demonstrated that contamination rates can be substantially reduced by collecting CB following caesarean delivery and utilizing trained collection staff. The majority of contaminating organisms in CB were shown to survive cryopreservation, storage and thawing. Additionally, the common practise of screening in a paediatric bottle proved suboptimal, particularly for anaerobic organisms. The optimal method of screening CB for microbial contamination was found to include a combination of discard fractions (plasma, RBC) and final product in an automated culture system utilising both aerobic and anaerobic culture bottles.