title: Bacterial contamination of anesthesia machines' internal breathing-circuit-systems.
abstract: BACKGROUND
  Bacterial contamination of anesthesia breathing machines and their potential hazard for pulmonary infection and cross-infection among anesthetized patients has been an infection control issue since the 1950s. Disposable equipment and bacterial filters have been introduced to minimize this risk. However, the machines' internal breathing-circuit-system has been considered to be free of micro-organisms without providing adequate data supporting this view. The aim of the study was to investigate if any micro-organisms can be yielded from used internal machines' breathing-circuit-system. Based on such results objective reprocessing intervals could be defined.
  
  
  METHODS
  The internal parts of 40 anesthesia machines' breathing-circuit-system were investigated. Chi-square test and logistic regression analysis were performed. An on-site process observation of the re-processing sequence was conducted.
  
  
  RESULTS
  Bacterial growth was found in 17 of 40 machines (43%). No significant difference was ascertained between the contamination and the processing intervals. The most common contaminants retrieved were coagulase negative Staphylococci, aerobe spore forming bacteria and Micrococcus species. In one breathing-circuit-system, Escherichia coli, and in one further Staphylococcus aureus were yielded.
  
  
  CONCLUSIONS
  Considering the availability of bacterial filters installed on the outlet of the breathing-circuit-systems, the type of bacteria retrieved and the on-site process observation, we conclude that the contamination found is best explained by a lack of adherence to hygienic measures during and after re-processing of the internal breathing-circuit-system. These results support an extension of the re-processing interval of the anesthesia apparatus longer than the manufacturer's recommendation of one week. However, the importance of adherence to standard hygienic measures during re-processing needs to be emphasized.
authors.affiliation: Clinical Institute for Hospital Hygiene, Medical University of Vienna, Vienna, Austria.
authors.forename: Verena
authors.initials: V
authors.lastname: Spertini
authors.forename: Livia
authors.initials: L
authors.lastname: Borsoi
authors.forename: Jutta
authors.initials: J
authors.lastname: Berger
authors.forename: Alexander
authors.initials: A
authors.lastname: Blacky
authors.forename: Magda
authors.initials: M
authors.lastname: Dieb-Elschahawi
authors.forename: Ojan
authors.initials: O
authors.lastname: Assadian