Duodenoscope contamination and decontamination: more questions than answers

Humans are populated by trillions of bacteria with their ratio to human cells being about 10:1 [1]. Whereas most bacteria, fungi, and viruses in humans live in perfect harmony and synergy, a few microorganisms may turn pathogenic if immunological or physical barrier disruption due to disease ensues. In addition, microbes may be introduced by external means, such as endoscopic procedures.

Endoscopy is an extremely rare cause of iatrogenic human microbial infection through direct inoculation or breakage of the protective boundaries such as mucosa, thereby allowing for microbial invasion. However, in the past there have been several outbreaks of duodenoscope-associated infections [2] [3] [4]. Root-cause analysis traced the cause of these outbreaks to improper post-endoscopic hygienic handling of the scopes [5]. Key steps in the hygienic process were skipped or wrongly performed. But proper cleansing of these duodenoscopes was also hampered by difficulties in accessing the Albaran elevator. Since scope cleansing practices were addressed, hygienic standards instituted, and mechanical improvements made to the elevators, no further outbreaks have been reported in the same institutions [6]. However, because most infections were blamed on the presence of biofilm in the duodenoscopes or highly pathogenic multidrug resistant pathogens, some nagging doubts about scope contamination or human incapacity to cleanse the scopes still persist.

Kwakman et al., from the Netherlands, set out an in vitro experiment to test contamination and decontamination mechanisms of duodenoscopes with a supraphysiological load of contaminated soil containing a mixture of four pathogens (Pseudomonas aeruginosa, Enterococcus faecium, Klebsiella pneumoniae and Escherichia coli) [7]. The scopes were placed on an S-tripod, the distal tip was inserted and soaked in a cup with 50 mL of the broth, a biopsy forceps was introduced 10 times into the working channel, the elevator was moved up and down 10 times, and the suction button was squeezed to suction the bacterial concoction into the scope, with the entire process lasting 10 minutes. The scopes were then cleaned and stored following current guidelines. Each scope channel was macroscopically investigated for scratches using a borescope a total of seven times.

“Although the results of this study may not have clinical applicability, they definitely do set up a basis for future studies of this topic, which by incorporating additional methodological, microbiological, and technical aspects could further improve our understanding of the interaction between microorganisms and endoscopes.”

The investigators collected microbiology specimens after high level disinfection and after overnight storage. Each scope was contaminated and cleaned 60 times, so a total of 180 contamination–decontamination cycles were performed. As each scope was cultured twice after each procedure, there were a total of 360 cultures available. Of these, 10 samples of the tip (5.7 %) were positive for any organisms, along with two of the post-drying samples (1.1 %). One duodenoscope showed persistent growth of P. aeruginosa from the fifth test until the end of the study. Interestingly, both the elevator and the distal tip of the contaminated scope were totally clean. The authors could not find any explanation for the persistent contamination in this one scope, and it led them to conclude that it was related to biofilm formation in its working channel.

The authors are to be commended for attempting to explore the mechanism of scope contamination by pathogenic microorganisms and their potential persistence after disinfection. Nevertheless, the study has some microbiological, technical, and clinical drawbacks that require further analysis.

First, from a microbiological standpoint, why were organisms not chosen and mixed based on prevalence? In this study equal quantities of four different pathogenic bacteria were mixed: P. aeruginosa, E. faecium, K. pneumoniae, and E. coli. However, clinical studies have shown that the most prevalent organisms are Enterococcus faecalis (33.2 %), E. faecium (28.6 %), and E. coli (23.2 %), whereas K. pneumoniae and P. aeruginosa were only present in 10.9 % and 5.9 % of bile samples, respectively [8]. Even Enterobacter cloacae (11.9 % of bile samples) was more commonly present than P. aeruginosa and K. pneumonia [8].

Another question that arose was the huge numbers of organisms used to create the infectious broth. The normal number of microorganisms in the duodenum is 100 000 organisms/mL [9], meaning the authors contaminated the scopes with up to 400 to 4000 times more bacteria (400 million organisms/mL) than are normally present in the duodenum [8]. This probably represents a scenario that is unlikely to be encountered in most clinical practices. It is also important to note that the receptacles storing the infectious broth may have also contained mature biofilm or sticky debris as it remained there for up to a week and was used during various contamination processes. Furthermore, the artificial soil contains elements such as cellulose and mucin, which may promote the formation or stabilization of biofilm.

The second aspect that calls for attention is from the technical standpoint as the way in which the duodenoscopes were contaminated does appear highly artificial and may not reflect clinical practice. It is unclear if the elevator was moved up and down in the presence of a biopsy forceps. Typically, biopsy forceps are rarely used in endoscopic retrograde cholangiopancreatography (ERCP). I would have chosen to use a biliary catheter or a sphincterotome. In addition, the forceps used was “reusable”. Could the use of a resterilized utensil have increased the risk of scope channel contamination?

Third, the experiment entailed that each cycle consisted of exposure of the duodenoscope to the experimental set-up, and that 60 of these cycles (or procedures) were done without any low grade bacteriological exposure cycles in between. This may not represent clinical practice, in which most ERCPs result in low grade exposure to contaminated bile or duodenal contents. The subsequent and additive effect of the cyclic nature of the experiment is another discrepancy with clinical practice, especially as many of these cycles showed that the duodenoscope was culture-positive, indicating that the scope was not completely disinfected.

Finally, the authors put in great effort in visually inspecting the scope channels and did not find scratches or damage to the inside. Nevertheless, it would have been interesting to have had objective visual or quantitative documentation of the absence or presence of biofilm. In addition, it would have been interesting to evaluate the post-cleaning results by using the soil manufacturer’s test kit, in which effective cleaning of endoscope surfaces and channels is deemed to have been achieved if there is < 6.4 µg of residual protein, < 1.8 µg/cm² of residual hemoglobin, and ≤ 4 log₁₀ viable bacteria/cm² [10]. As a result, we do not know if the scopes really do promote bacterial growth or if growth is promoted by improper scope cleaning and drying. Based on all outbreaks of ERCP-associated infections so far, we know that poor scope cleaning practices and breaches in hygienic standards and proper drying have been the culprits of the outbreaks [5]. The proof is that all outbreaks ceased after hygienic practices and proper drying methods were implemented [6].

In summary, the authors are to be congratulated for attempting to further elucidate the mechanisms of duodenoscope contamination and decontamination. Although the current results may not have clinical applicability, they definitely do set up a basis for future studies of this topic, which by incorporating additional methodological, microbiological, and technical aspects could further improve our understanding of the interaction between microorganisms and endoscopes.

Publication History

Article published online:
21 July 2022

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