The Congress of the German Society for Hospital Hygiene, which took place from 12 to 14 April as an online-only event, featured two sessions on medical device reprocessing. The first lectures dealt with reprocessing of thermolabile flexible endoscopes.
Rapid detection method for GA
Markus Wehrl from the wfk Cleaning Technology Institute presented a rapid detection system for glutaraldehyde residues on flexible endoscopes. The treatment of thermolabile endoscopes is carried out by cleaning and chemo-thermal disinfection. In Germany, 80% of processes use glutaraldehyde (GA). Glutaraldehyde residues can come into contact with mucous membranes during subsequent endoscopy and cause inflammatory reactions, e.g. GA-associated colitis. GA residues must therefore be removed as completely as possible; based on data from animal models, a limit value of 1.5 micrograms/cm2 has been set.
Regular checks on GA residues are required according to the German KRINKO and BfArM guideline, but the laboratory tests are complex, relatively expensive and time.
Now a rapid monitor system has been developed based on the use of enzymes immobilized on a membrane carrier, which in combination with a special enzyme substrate lead to coloured reaction products. In the presence of GA residues, the colour disappears – this reaction is highly specific to GA.
The enzyme system is pressed onto sampling points of the endoscopes for 10 minutes. The colour change can be used to determine whether GA residues exceeding the limit value are present on the sampled area.
What is the situation in practice? A total of 11 treated endoscopes were sampled in three hospitals. Six endoscopes with critical residues were found, so it can be assumed that the problem is more widespread than suspected, Wehrl said.
Due to its simple and fast applicability, the new detection system is suitable as a routine check in the reprocessing units. It reliably indicates insufficient final flushing, or changes of the medical device’s surface (e.g. due to aging), which are associated with high adsorption of GA. A similar system for the detection of GA and peracetic acid is currently under development.
Biofilm – the advantages of pH-neutral peracetic acid
Afterwards, Florian Brill explained the advantages of pH-neutral peracetic acid compared to peracetic acid with regard to the reduction of viable microorganisms in biofilms. Biofilms pose a particular challenge, especially when reprocessing flexible endoscopes, and can only be removed to a limited extent by high-level disinfection.
Peracetic acid is often used to reprocess flexible endoscopes and has advantages over glutaraldehyde – due to the reduced protein fixation, biofilm formation in the endoscope is less likely.
To investigate the benefits of pH-buffered peracetic acid with regard to the removal of biofilm, unbuffered and pH-buffered peracetic acid solutions were compared with respect to their potential to reduce the colony count of biofilms. For this purpose, biofilms of Pseudomonas aeruginosa PA 14 (DSM 19882) were incubated on microtiter wells. The biofilms were used after 24 hours or after 72 hours to simulate the situation on a working day or on weekends, respectively. On weekends, after an emergency intervention, it may take longer until the reprocessing process is started.
Different peracetic acid concentrations were tested at a temperature of 39 °C with a contact time of 5 minutes – this was supposed to simulate typical conditions in an RDG, explained Brill.
It turned out that the 24 h-old biofilms could be removed almost completely by treatment with both buffered and unbuffered peracetic acid. On the other hand, the 72 h-old biofilms were more robust and could not be completely removed by the respective solutions. However, buffered peracetic acid proved to be significantly more effective.
This may be due to the fixation of extracellular polymeric substances (EPS) by the unbuffered disinfectant solution. Acidic pH could promote coagulation of biofilm polymers, thus representing a greater barrier to the disinfectant and protecting the bacterial cells. Buffered (pH-neutral) peracetic acid can therefore have advantages over acidic formulations when removing aged biofilms.
Above all, however, the results also show that the longer storage of flexible endoscopes before reprocessing should be avoided.
Flush – brush – flush for better results
As part of the validation of automated reprocessing processes for flexible endoscopes, the microbiological evaluation of treated endoscopes after real use is carried out in accordance with Annex 10 of the guideline of DGKH, DEGEA, DGSV, DGVS and AKI. For this evaluation, rinsing samples of all endoscope channels are taken and the total number of microorganisms as well as the number of potentially pathogenic microorganisms are determined. Markus Wehrl in his talk dealt with the development of optimized methods for microbiological sampling of endoscope channels.
It was investigated whether the composition of the elution medium used for the extraction of the flushing samples has an influence on the recovery rate of microorganisms. Recovery rates that are too low would lead to an underestimation of risk.
Using a test specimen model (PTFE hose, contaminated with reactivated, coagulated sheep blood and Enterococcus faecium), recovery rates were determined in nine participating laboratories after using sodium chloride, DNP, FHM and T+Thio solutions. The results in this round robin test showed no significant differences in the recovery rates determined in the different laboratories.
Further experiments have investigated the use of brushes and repeated rinsing. Wehrl presented the design of such an experiment using the flush-brush-flush method. This approach can increase the recovery rate for microorganisms by a factor of 25 compared to simple flushing. The revised method is now to be established as quickly as possible.
Developing test methods for detergents
Markus Wehrl also reported on the work of the DGKH Working Group for Testing Detergents. While test methods for cleaning processes are well-described, there are no generally accepted test methods for instrument cleaners. The Working Group tries to develop test methods for this purpose.
Wehrl reported on the development of a test model based on fibrin as a test soil for the comparative evaluation of the efficacy of detergents for manual cleaning. Based on the development of an innovative elution method, the water-insoluble fibrin soil on the PCDs can be converted into a solubilized form and measured using traditional protein quantification methods (OPA, BCA method).
Reproducibility of the production of the fibrin test specimens and the application in cleaning tests was confirmed in several comparative tests with six participating laboratories.
The new test model allows for comparative testing of the efficacy of different detergents in an immersion model (no mechanical action) and is able to differentiate various instrument detergents in terms of their efficacy.
More testing is currently underway: the Working Group uses the fibrin test specimen to determine acceptance criteria for detergents for manual cleaning. A large number of different detergents is currently examined for this purpose.
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