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Does Enhanced Sterilization of Duodenoscopes Reduce Contamination?

comparison of duodenoscopes reprocessed by standard high-level disinfection (sHLD) vs double high-level disinfection (dHLD) and standard high-level disinfection followed by ethylene oxide gas sterilization (HLD–ETO) found no significant differences in contamination with multidrug-resistant organisms (MRDO) or other bacteria. The article, published in the October issue of Gastroenterology, concludes that enhanced disinfection methods do not provide additional protection against contamination.

Duodenoscopes have been implicated in transmission of multi-drug resistant bacteria. Experts have recommended adopting additional measures like double reprocessing cycles and ethylene oxide sterilization to supplement current standards. However, the effectiveness of these additional measures has never been systematically studied in a non-outbreak setting.

Graham M. Snyder et al performed a prospective, randomized trial to compare the frequency of duodenoscope contamination with MRDO or any other bacteria after disinfection or sterilization by sHLD, dHLD, and ETO.

The authors randomly reprocessed duodenoscopes at their tertiary care center by sHLD, dHLD, or HLD–ETO. Samples were collected from the elevator mechanism and working channel of each duodenoscope and cultured before use. Snyder et al then determined the proportions of duodenoscopes with culture showing 1 or more MDRO, as well as the frequency of duodenoscope contamination with more than zero and 10 or more colony-forming units (CFU) of aerobic bacterial growth on either sampling location.

After collecting data for 3 months, the authors stopped the study because they did not observe sufficient events to evaluate their primary outcome.

In analysis of 516 cultures from duodenoscopes, none were found to be positive for MDRO. Bacterial growth of more than zero CFU was found in 16.1% duodenoscopes in the sHLD group, 16.0% in the dHLD group, and 22.5% in the HLD–ETO group.

Some experts have suggested that ethylene oxide sterilization increases the likelihood of damage to duodenoscopes. Snyder et al propose that this might have contributed to the contamination observed in a higher proportion of duodenoscopes reprocessed by HLD–ETO.

Bacterial growth or 10 or more CFU was found in 2.3% of duodenoscopes in the sHLD group, 4.1% in the dHLD group, and 4.2% in the HLD–ETO group. No duodenoscopes met pre-specified criteria for persistent duodenoscope contamination.

Among the 389 patients undergoing at least 1 procedure during the study, 26 patients had a history of infection with ≥1 MDRO before study participation. MRDOs were cultured from 3.2% of pre-procedure rectal swabs and 2.5% of duodenal aspirates. These findings indicate that in the non-outbreak setting, sHLD adequately disinfects duodenoscopes, even when they have been used for patients with MDRO infection.

Regression analysis showed no association between study group and frequency of duodenoscope contamination when more than zero CFU of bacterial growth was used as the outcome variable. The authors found no significant association between the enhanced sterilization procedures and contamination—even after adjusting for duration of preceding procedure, sphincterotomy, stent removal, and time elapsed between preceding procedure and repeat culture. So, instrumentation of the biopsy channel does not appear contribute to duodenoscope damage or contamination.

Snyder et al claim that this was the first prospective randomized trial comparing sHLD, dHLD, and HLD/ETO for reprocessing duodenoscopes. In their non-outbreak setting, they found no significant difference between these methods with regard to proportion of duodenoscopes with MDRO contamination, or demonstrating 10 or more CFU or more than zero CFU growth of any aerobic bacteria. MDRO were not recovered from any duodenoscope cultures, which limited their ability to detect differences between reprocessing methods.

A previous study reported that 3 of 4 duodenoscopes contaminated with drug-resistant Escherichia coli were damaged and needed repairs. However, these duodenoscopes did not demonstrate functional problems and the defects were not recognized until the duodenoscopes were returned to the manufacturer. It is not known if dHLD or HLD–ETO sterilization can disinfect structurally defective duodenoscopes.  Snyder et al propose that endpoints for future studies of duodenoscope reprocessing should include analyses of handling, storage, and possible structural damage to duodenoscopes.

Snyder et al add that duodenoscope contamination might be perpetuated by biofilms that sustain viable bacteria. Biofilm has been identified within endoscope channels following reprocessing, and studies that used adenosine triphosphate to detect organic matter found biofilm could account for the inability of culture tests to detect viable bacteria, particularly in the elevator mechanism. The authors propose that future studies include culture results and measurement of biofilms.

In an editorial that accompanies the article, V. Raman Muthusamy writes “How do we prove that a reprocessed device is actually clean?” The optimal methods and techniques for doing this are not clear, but are required to accurately assess the different reprocessing techniques. These might include collecting culture samples from the elevator recess area, scope tip, and endoscope channels; testing samples obtained from the same areas for residual biological material (via adenosine triphosphate tests); or even direct visual inspection of the channels for residual biologic material, biofilm, or evidence of mechanical damage.

Muthusamy proposes development of new methods that can safely and efficiently sterilize duodenoscopes, such as liquids or gases that are not impaired by biofilm, or development of duodenoscopes that can withstand high temperatures and could be autoclaved. Finally, a disposable device could be the ultimate solution to eliminate the risk of duodenoscope-associated transmission of infections, although there are significant challenges to making an affordable device that is of comparable quality to existing equipment.

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Kristine Novak

Kristine Novak

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About The Author:

Dr. Kristine Novak

Dr. Kristine Novak

Dr. Kristine Novak is a science writer and editor based in San Francisco. She has extensive experience covering gastroenterology, hepatology, immunology, oncology, clinical, and biotechnology research discoveries.

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