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.