DECONTAMINATION & STERILISATION
with positive (spiked) samples, as well as a standard curve with each test, so that the colour change can be directly correlated to a certified reference standard endotoxin.
The user should be aware of the different methods to assess the suitability. Gel clot tests: These are normally carried out in a test tube, and can be limit tests (not quantitative), or semi quantitative methods. The test relies on the operator observing the lysate clotting into a firm gel, and so may be subject to inter-operator variability. If the test fails the specification, it may be expressed simply as ‘greater than’ the sensitivity of the test, and these results may not always be meaningful, dependent on the specification being applied. Photometric and chromogenic techniques: The reaction of the lysate in these tests can be more quantitively measured by the development of a turbidity or colorimetrically. These are often in conjunction with a microplate reader, so that the correlation of the reaction onset time can be automatically correlated to traceable endotoxin value. Most of these methods are based on the British/European Pharmacopoeia standard methods, considered the gold standard for this test. As with all subcontracted laboratory analysis, the user should seek reassurances that the laboratory has UKAS accreditation for the testing method. This ensures that the quality management system is in place to control and monitor operator training, proficiency testing schemes, and method validation.
Residual chemicals
Washer-disinfectors use several chemicals as part of the cycle – namely detergents, disinfectants, and rinse aids. These must be removed by rinsing with water during several points in the process to ensure that chemicals do not carry over into the next stage and potentially reduce the activity of disinfectants and other chemicals. Furthermore, instruments must be free from unintended chemical contamination after the process. Testing the rinse water will give a measure of the level of residues compared with the ‘control’ source water sample. The two main methods for assessing residual chemicals are: n Total Organic Carbon (TOC) – Almost all detergents and disinfectants will contain organic carbon, this can be determined by laboratory analysis.
n Electrical Conductivity – Dissolved ions from process chemicals remaining in the rinse water will decrease the electrical resistance of the water, and increase the conductivity reading. Comparison of the two readings can determine the relative level of residues.
136 Health Estate Journal October 2019
These methods will help to ensure that the instruments remain free from chemical residues; however, other methods can be recommended by the manufacturer that may be more specific to the chemical used in the process. Some process chemicals are permitted in the final rinse water, as they are intentionally added to discourage microbial proliferation in the rinse water. These may include low-level disinfectants such as chlorine-based compounds that have been demonstrated to be non-toxic, or at a low enough concentration. Off-the- shelf test kits or monitoring strips may be used to routinely check the levels present in the final rinse water.
Air monitoring
Chemicals used in the process may produce hazardous gases and become a risk to the operator. Monitoring can be performed periodically, or with fixed equipment, to ensure that work exposure limits are not being exceeded during the process. It is a requirement of the HTM to ensure both yearly, and on revalidation, that chemical vapours are measured using gas monitoring equipment. This is usually with sensors that measure the infra-red absorption by the gas, or with an electrochemical sensor, dependent on the type of gas. This testing may not be part of the main EWD service and validation schedule, so the user should seek out an independent testing provider.
Disinfection efficacy and surrogate devices
In thermal washer-disinfectors, disinfection efficacy is a relatively straightforward measurement of the temperature. Endoscope washer-disinfections, however, can have many more factors which affect the chemical disinfection. Routine microbiological testing of the disinfection efficacy has been removed from the latest guidance, which means that potential disinfection problems may go unnoticed. The current alternative test method is to sample endoscopes for natural contamination that remains after the process, as opposed to inoculating a surrogate device with live organisms. This is currently recommended only if a problem is suspected. The AE(D) or user may request the disinfection efficacy is proven using the method described in ISO 15883 Part 4 to demonstrate that the washer disinfector is still performing in accordance with its original type testing.
The user should be aware that there are a large variety of surrogate devices being used on EWDs, and that not all of them accurately mimic an endoscope. According to the international standard, the surrogate device should contain trumpet valves and connection ports so that the fluid pathway reflects the actual instrument and connection method.
Drying cabinets and storage systems: These pieces of equipment are often less complex in design than an endoscope washer-disinfector, but still have a significant risk associated with them if not properly used and maintained. Surrogate devices used in these systems need to reflect the complexity of the internal channels, which can make drying significantly more difficult than a unbifurcated length of tubing. Testing conditions should control for factors that present a risk, such as connection methods and the initial state of the endoscope, which will have an unknown residual volume of water present from the EWD process. Furthermore, this residual water is not guaranteed to be free of bacteria. A sterile, dry length of tube will not adequately control for this initial state. If surrogates are to be used in place of endoscopes during routine testing, then the requirement Annex E2 of EN 16442:2015, to clean and disinfect beforehand according to the ‘procedure in force in the unit’, would better reflect actual conditions.
In conclusion, users should be cautious in replacing test methods purely because it is more cost-effective or a new technology. If possible, carry them out side by side, and seek the advice of the AE(D) until the method is incorporated into the official guidance. Current testing methods should be constantly reviewed, as the fast pace of development in these areas means they may quickly become obsolete or non-compliant.
References 1 Parohl et al. Monitoring of endoscope reprocessing with an adenosine triphosphate (ATP) bioluminescence method. GMS Hygiene and Infection Control, 2017.
2 Friter et al. OPA method modified by use of N, N-dimethyl-2- mercaptoethylammonium chloride as thiol component. Fresenius Journal of Analytical Chemistry, 1988.
3 Lipscomb et al. The sensitivity of approved Ninhydrin and Biuret tests in the assessment of protein contamination on surgical steel as an aid to prevent iatrogenic prion transmission. Journal of Hospital Infection, 2006.
David Woods
David Woods BSc (Hons) has been the Operations Manager for T.E.S.T. since 2014, and is an Authorised Person (Decontamination). Since university he has worked as a microbiologist, and managed sterilisation and washer-disinfector validation processes as part of the range of independent services offered by T.E.S.T.
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