Factors affecting microbial contamination rate of cord blood collected for transplantation

Collection and processing of cord blood (CB) is associated with significant risk of microbial contamination and hence relevant standards mandate microbial screening of the final product. This study aimed to determine the contamination rate and associated risk factors during 14 years of banking at the Sydney Cord Blood Bank.

CB was collected and processed using a closed system and tested for contamination using blood culture bottles (BacT/ALERT, bioMérieux) incubated for a minimum of 5 days. Four microbial screening methods were used with different combinations of inoculated bottles (adult or pediatric) and associated sample volumes (10 or 1 mL).

Of 13,344 CB units screened, 537 (4.0%) tested positive for contamination, with Bacteroides spp. (20.9%), Staphylococcus spp. (18.6%), and Propionibacterium spp. (13.7%) being the most common isolates. The contamination rate reduced from 10% in 1997 to 1.1% in 2009. Multivariate analysis demonstrated the following variables were independently associated with higher contamination rates: vaginal delivery, collection by obstetric staff, and use of an anaerobic bottle in addition to an aerobic bottle (which facilitated a larger sample inoculation volume than pediatric bottles).

This study demonstrates that contamination rates of CB collected for transplantation can be substantially reduced by collection after cesarean delivery and utilizing trained CB collection staff. These data also indicate that the common practice of testing using a pediatric (aerobic) bottle with its attendant small volume of the final CB product may be suboptimal for sensitive detection of contaminating anaerobic microbes.