Liquid nitrogen freezers: a potential source of microbial contamination of hematopoietic stem cell components
Abstract
The recent report of hepatitis B transmission between hematopoietic progenitor and putative stem cell (HPC) components stored in liquid nitrogen led to the questioning of whether evidence existed for similar contamination by bacterial or fungal elements. Microbial contamination rates were reviewed for 704 HPC components from 255 patients over an 18-month period. Five liquid nitrogen freezers were surveyed for microbial contamination. The literature was reviewed to ascertain the published experience of other laboratories with HPC component contamination first documented on thawing. Seven (1.2%) of 583 thawed components were found to be contaminated with a variety of environmental or waterborne organisms, despite a meticulous protocol to prevent contamination during thawing. All of these components had been sterile on cryopreservation. Literature review revealed a similar incidence of post-thaw contamination from other centers. Microbial survey of liquid nitrogen freezers revealed low-level contamination in four of five. The organisms represented were similar to those cultured from thawed HPC components. One freezer was heavily contaminated by Aspergillus species. Liquid nitrogen freezers are not sterile, and both the liquid and ...Continue Reading
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