The Disinfection and Sterilization of Endoscopes: A Primer

A 2013 study assessed 98 endoscopy-related outbreaks in which 1,113 patients were contaminated and 249 infected.1 More recently, > 130 gastrointestinal outbreaks were cited and > 25 outbreaks of MDROs (multi drug-resistant organisms) in the U.S. associated with extensive morbidity and mortality related to contaminated duodenoscopes.2,3

As one researcher noted: “Exogenous infection due to contaminated endoscopes is the most common cause of device related nosocomial infection in the U.S.”2

Principles guiding disinfection and sterilization from Spaulding4 date back to 1968, in which the level of disinfection or sterilization is dependent on intended use:

  • Critical – items that contact sterile tissue, e.g., surgical instruments.
  • Semi-critical – contact mucous membranes, such as endoscopes.
  • Non-critical – contact only intact skin, such as stethoscopes.

These classifications require sterilization, high-level disinfection, and low-level disinfection, respectively. Automated washer-disinfectors (WDs) are commonly employed, though manual cleaning must be used for some delicate surgical instruments or endoscopes.3

Critical items are processed by steam sterilization unless heat-sensitive. If the latter, they may be treated with ethylene oxide (EO), hydrogen peroxide gas plasma, vaporized hydrogen peroxide, hydrogen peroxide vapor and ozone, or liquid chemicals. Liquid sterilant efficacy depends on adherence to guidelines as to concentration, contact time, temperature, and pH.5

While the Spaulding scheme remains valid today, concerns regarding disinfection with respect to prions, viruses, mycobacteria, and protozoa have renewed considerations.5 In fact, in May 2015, a Food and Drug Administration (FDA) panel reclassified duodenoscopes from semi-critical to critical to support a shift from high-level disinfection to sterilization.5

Cleaning, Sterilization and Testing: Steps to Assurance

An additional consideration is that surgical instruments and endoscopes differ relatively in the targets for cleaning and processing. Surgical instruments usually have a low microbial load and a high organic load after use.6 Organic residuals include patient secretions, tissue, bone and blood. Endoscopes, in contrast, tend to have low organic and high microbial loads. Cleaning must always precede disinfection and sterilization to remove contamination.

Endoscopes are particularly problematic because many have long narrow channels and right angle turns.3 This makes it difficult to clear of all contamination. Further, inability to assure complete drying of the channels, despite alcohol and air flush, contributes to higher microbial levels and supports biofilm formation.2,3,6 This may result in remaining contamination even in fully reprocessed duodenoscopes.7

Although evidence for infection transmission from sterilized surgical instruments is less robust than for disinfected endoscopes, it still highlights the role that biofilm or retained secretions and tissue may play if cleaning is not effective; thus, the need for appropriate testing methods to stringently assess the efficacy of disinfection.2

It is now recognized that contaminated non-critical patient care items and environmental surfaces can play a role in the transmission of health care-associated pathogens such as methicillin-resistant Staphylococcus aureus, and Clostridium difficile.8 As such, disinfection in this category is important as is surveillance testing.

Quality Management Systems applied to medical device processing incorporate validated cleaning protocols and monitoring to assure adequacy of such cleaning.6 Disinfection and sterilization processes fail if the cleaning has not been performed adequately.6

Tests that monitor cleaning detect microbial or organic residuals and may include ATP (adenosine triphosphate), total organic carbon, protein, carbohydrate, enzymes specific to gram negative bacteria, or hemoglobin.3,6 Tests for ATP are measured as reactive light units (RLUs) and differ among test kits.

It is important to use facility-set benchmarks for determining cleaning adequacy because even low RLU values in an ATP test may offer a false sense of security in that a significant microbial load could remain (it takes ~100-1000CFU to generate a signal of 1 RLU).3,6

The complicated challenges associated with the cleaning and sterilization of endoscopes will continue until appropriate disposable scopes become an affordable and available reality. In addition, EO sterilization is under critical review globally, especially because of environmental concerns/human toxicity related to release of byproducts into the atmosphere during manufacture. Research into a replacement for EO sterilization is active.

Want more information about sterilization and cleaning monitoring? Read about the tools 3M offers to ensure endoscopes and other medical instruments remain safe between use.

1 Kovaleva J et al. Transmission of infection by flexible gastrointestinal endoscopy and bronchoscopy. Clin Microbiol Rev 2013; 26: 231-54.
2 Alfa MJ. Biofilms on instruments and environmental surfaces: Do they interfere with instrument reprocessing and surface disinfection? Review of the literature. AJIC.2019; 47: A39-A45.
3 Rutala WA et al. What’s new in reprocessing endoscopes: Are we going to ensure “the needs of the patient come first” by shifting from disinfection to sterilization? AJIC 2019 47: A62-A66.
4 Spaulding EH. Chemical disinfection of medical and surgical materials. In: Lawrence C, Block SS, eds. Disinfection, sterilization, and preservation. Philadelphia: Lea & Febiger, 1968:517-31.
5 Rutala WA and Weber DJ. Disinfection, sterilization, and antisepsis: An overview. Am J of Infection Control. 2019: 47: A3-A9.
6 Alfa MJ. Medical instrument reprocessing; current issues with cleaning and cleaning monitoring. Am J of Infection Control. 2019; 47: A10-A16.
7 Rauwers AW et al. High prevalence rate of digestive tract bacteria in duodenoscopies: a nationwide study. Gut. 2018; 67: 1634-45.
8 Rutala WA and Weber DJ. Disinfection, sterilization, and antisepsis: Principles, practices, current issues, new research, and new technologies. Am J Infection Control. 2019; 47: A1-A2.

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