Discussion
Current reprocessing methods with the EWD are time-consuming and UV-C light disinfection seems a promising alternative. However, a study comparing UV-C light disinfection of FEs without a working channel with the EWD was still missing.
Guidelines describing disinfection methods determined that a log 4 reduction in CFU formation after disinfection is considered an acceptable disinfection method(17). In our study, the Agar plates were contaminated with CFUs in a wide range, often less than 100 CFUs. Therefore, it was not possible to achieve a log 4 reduction. In previous research, a threshold of ≤ 2.5 CFUs/cm2 on agar contact plates was considered acceptable based on food preparation standards(18). The ESGE accepts a maximum total microbiological count of <20 CFUs for fluid collected after flushing the endoscope. Quantification of microorganisms is not recommended for cultures taken from the outer surface of the endoscope, suggesting that the policy should be based on the growth of indicator organisms(19). Since there is no consensus on the acceptable CFUs count on FEs without a working channel after disinfection, we agreed that 0 CFUs after disinfection was considered a safely disinfected FE.
In total, 12 FEs in group 1(D60) and 13 FEs in group 2(EWD) were still contaminated after disinfection. However, since no bacterial identification was performed, no statements can be made about whether bacteria found were commensal flora or pathogens.
In three FEs(1 D60, 2 EWD), the culture after disinfection showed a higher number of CFUs than before disinfection. This can be explained by several reasons. First, the study took place under clinical conditions, where handling the FEs under unsterile conditions may have affected the results. Second, the contamination could have been caused by the disinfection method (D60 or EWD) or during transportation to the second culture taking. The most plausible reason is the limited sensitivity of the culture method.
There is no standardized method for culture collection from FEs. Methods used to determine surface contamination include swabs, contact plates, sponges, broths, quantitative polymerase chain reactions and dip slides(20). Specific guidelines for culturing ORL endoscopes do not exist, but several organizations such as the ESGE, the European Society of Gastroenterology and Endoscopy nurses and Associates(ESGENA) and the Gastroenterological Society of Australia provide recommendations for microbiological monitoring of FEs(19, 21). However, their suggested sampling methods include liquid samples from endoscope channels, which is impossible for FEs without a working channel. The ESGE-ESGENA guideline additionally recommends a swab method to evaluate the contamination of the surface of the endoscope(19). Prior to this study, we conducted a pilot comparing three commonly described sampling methods, which will be submitted shortly. The three sampling methods compared were: a rolling method on an Agar plate, swab method and broth method for sampling FEs without working channel. We found that all sampling techniques were capable of detecting microbiological contamination. However, practical difficulties lead to a preference for the rolling technique.
Previous studies investigating UV-C light disinfection in ORL showed a high bacterial load with an average value of 66.908 CFUs and 916.7 CFUs(13, 14). This is inconsistent with the contamination found in this study on the FEs after clinical use. A possible explanation could be that Rudhart et al (13) used rigid endoscopes, which have a different surface texture than FEs. Due to the surface properties and flexible property of the FEs, the rolling method may be easier to perform on the rigid endoscope than on the FEs. In the following study by Rudhart et al(14), the FEs were sampled directly after clinical use. In our study, the FEs first underwent pre-cleaning before sampling. The pre-cleaning may have already reduced microbiological contamination, resulting in lower bacterial contamination.
In addition to the advantage of time reduction, UV-C light disinfection has additional advantages. UV-C light disinfection does not use water or chemicals except for pre-cleaning. Because of the short disinfection process, fewer FEs and storage capacity are needed. These factors contribute to a reduction in costs and environmental impact.
Limitations of this study were that we did not investigate non-bacterial pathogens on the FEs. Literature described some cases of viral and fungal cross-contamination in gastrointestinal endoscopic procedures(22). Presumably, ORL FEs without a working channel also carries the potential to transmit viral or fungal pathogens. Previous research has shown that UV-C light has the potential to inactivate viral and fungal pathogens(11, 23). Based on previous research, it is very unlikely that a FE carries the potential to transmit prion disease(24). Previous research has shown that the absorption spectra of peptide bonds in prions are between 190 and 230nm, indicative of susceptibility to UV light. Further research is needed to determine the UV susceptibility(25). Furthermore, we did not perform a bacterial identification. Thus, we cannot make any statements about whether the bacteria found were commensal flora or pathogens. The efficacy of UV-C light disinfection greatly relies on the manual pre-cleaning since UV-C light cannot penetrate through dirt, debris and grime. Since the pre-cleaning is a manual process, the quality of the pre-cleaning may vary per person performing the process. Thus, when UV-C light disinfection is implemented, the process of manual pre-cleaning requires extra attention in the instruction for employees who will perform the UV-C light disinfection. This could have led to a potential bias in our study. Due to the logistical decision of the hospital to move the disinfection process of FEs without a working channel to the centralized reprocessing department, some FEs in group 2 were centrally reprocessed. These FEs were additionally pre-cleaned with Neodisher® MediClean forte (Dr. Weigert Nederland B.V., Assen, The Netherlands). However, after reprocessing, CFUs counts showed no marginal gain for using centralized reprocessing over decentralized reprocessing in the EWD. Finally, we did not perform a power analysis for the number of FEs studied. The study group is relatively small and the results should be confirmed with a larger sample size in a multicenter setting.