title: Liquid nitrogen freezers: a potential source of microbial contamination of hematopoietic stem cell components.
abstract: BACKGROUND
  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.
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  Liquid nitrogen freezers are not sterile, and both the liquid and vapor phases are potential sources of microbial contamination of HPC components. While low-level contamination by environmental organisms may be common, the occurrence of heavy contamination by potential pathogens such as Aspergillus species suggests that monitoring of liquid nitrogen sterility may be indicated. Strategies to assess and prevent microbial transmission from liquid nitrogen to HPC components need further development.
authors.affiliation: Brigham and Women's Hospital, Beth Israel Deaconess Medical Centèr, Boston, Massachusetts, USA.
authors.forename: D
authors.initials: D
authors.lastname: Fountain
authors.forename: M
authors.initials: M
authors.lastname: Ralston
authors.forename: N
authors.initials: N
authors.lastname: Higgins
authors.forename: J B
authors.initials: JB
authors.lastname: Gorlin
authors.forename: L
authors.initials: L
authors.lastname: Uhl
authors.forename: C
authors.initials: C
authors.lastname: Wheeler
authors.forename: J H
authors.initials: JH
authors.lastname: Antin
authors.forename: W H
authors.initials: WH
authors.lastname: Churchill
authors.forename: R J
authors.initials: RJ
authors.lastname: Benjamin
mesh_terms: D000151:Acinetobacter Infections / Q000635:transmission; D001854:Bone Marrow Cells; D015925:Cryopreservation / Q000295:instrumentation* / Q000379:methods; D004340:Drug Contamination; D006412:Hematopoietic Stem Cells / Q000382:microbiology; D006801:Humans; D009584:Nitrogen; D013242:Sterilization; D065227:Transfusion Reaction
chemical_list: D009584:Nitrogen