Quantitative analysis of residual protein contamination on reprocessed surgical instruments
Introduction
Decontamination in medical instrument reprocessing is one of the major challenges facing healthcare facilities. This has been highlighted in several official reports.1, 2 There is now a body of scientific literature concerning residual tissue contamination on specific surgical instruments and cases of nosocomial infections.3, 4, 5, 6 Concerns have also been expressed with respect to bacterial contamination and pyrogens.7, 8, 9 In this context, the potential risk of iatrogenic transmission of Creutzfeldt Jacob disease is noteworthy, as the infectious agent shows a marked resistance to conventional chemical and thermal decontamination procedures and has been shown to bind to stainless steel.10, 11, 12, 13, 14, 15, 16, 17, 18 Perversely, however, virtually no quantitative data are available on the amount of tissue-derived material that typically remains on instruments after cleaning and sterilization by modern hospital decontamination procedures. This may derive from the degree of tenacity by which some tissue residues bind to surfaces. A criticism of the majority of previous studies is that they fail to characterize tissue contamination found by superficial inspection, or they confound the results by removing soil with detergents before semi-quantification by filtration and/or assay of the cleaning solution.
As part of a survey commissioned by the UK Department of Health, trays of sterile reprocessed surgical instruments, chosen at random from the sterile services departments (SSDs) of several National Health Service hospital trusts in England and Wales, were removed from service and analysed for contamination. A destructive method was used to remove all surface contamination from the instrument surfaces, and the bound protein was quantified after hydrolysis to its constituent amino acids. The present study reports on the results from five individual instrument trays (comprising a total of 120 instruments), each of which was processed in a different SSD. This is the first study to provide quantification of the total amount of proteinaceous contamination that persists in adhering to instruments after routine hospital cleaning and sterilization, and to provide reliable data on which future risk assessments might be based.
Section snippets
Scanning electron microscopy
Detailed microscopic inspection of eight instruments from each tray was conducted using a Philips XL30CP instrument, operating at 20 kV, providing a resolution better than 5 nm. Backscatter electron imaging enabled regions with a mean atomic number difference of greater than 0.1 to be resolved.
Energy dispersive X-ray spectroscopic analysis
Energy dispersive X-ray spectroscopic analysis (EDX) was carried out in a scanning electron microscope (SEM) using an Oxford Instruments Isis 300 X-ray analyser, capable of detecting elements of atomic
Results
The results of complete surface protein analysis for each tray of instruments are shown in Table I. Results for specific instruments are given in the supplementary data on ScienceDirect (see Appendix).
Protein levels varied significantly between the five trays (P < 0.001). Trays 1–3 did not show a significant difference from one another, while the difference between Trays 4 and 5 was just significant (P = 0.03). There was no significant correlation between instrument complexity (as judged on a
Discussion
Previous studies on evaluation of residual contamination on surgical instruments fall into three categories: (1) visual or microscopy examinations of instrument surfaces;3, 5, 6 (2) exhaustive washing and measurement of contaminants in the washings;4 and (3) sampling small areas of the surfaces by swabbing and analysis of contamination on the swab or swab washings.20, 21, 22
Visual examination and microscopy can, at best, give an indication of heavily contaminated sites but can hardly be
Acknowledgements
The authors received funding from the Department of Health for this study. The views expressed in the publication are those of the authors and not necessarily those of the Department of Health. The authors wish to thank John Craven and Nicola Cayzer of the SEM facility, Geology and Geophysics, University of Edinburgh.
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2017, Research in Veterinary ScienceCitation Excerpt :Preconditioning layers of adsorbed organic material on stainless steel surfaces and residual infectious proteinaceous contamination of surgical instruments can promote adhesion of pathogenic microbial agents such as S. aureus (Banerjee et al., 2010; Barnes et al., 1999; Lipscomb et al., 2006). Despite commonly applied cleaning and sterilization procedures to various surgical instruments of different size and shape, studies found a substantial percentage of remaining proteinaceous and non-proteinaceous contamination (by visual inspection and microscopic evaluation) after staining (Banerjee et al., 2010; Baxter et al., 2006; Lipscomb et al., 2006; Murdoch et al., 2006; Smith et al., 2011; Smith and Smith, 2012). The washing and sterilization process used for drill bits in this study followed the standard protocol of the clinic, but whether proteinaceous residues were present on the drill bits after the blood coating experiment was not documented.