Cleaning and Disinfecting Gastrointestinal Endoscopy Equipment

Cleaning

Cleaning refers to removal of visible soiling, blood, protein substances, and other adherent foreign debris from surfaces, crevices, and lumens of instruments. It is usually accomplished with mechanical action using water, detergents, and enzymatic products. Meticulous physical cleaning must always precede disinfection and sterilization procedures, because inorganic and organic materials that remain on the surfaces of instruments interfere with the effectiveness of these processes. Mechanical cleaning alone reduces microbial counts by approximately 10 ³ to 10 ⁶ (three to six logs), equivalent to a 99.9% to 99.9999% reduction in microbial burden.

Sterilization

Sterilization is defined as the destruction or inactivation of all microorganisms. The process is operationally defined as a 12-log reduction of bacterial endospores. Not all sterilization processes are alike, however. Steam is the most extensively utilized process and is routinely monitored by the use of biologic indicators (e.g., spore test strips) to show that sterilization has been achieved. When liquid chemical germicides (LCGs) are used to eradicate all microorganisms, they can be called chemical sterilants; however, the US Food and Drug Administration (FDA) and other authorities have stated that these processes do not convey the same level of assurance as other sterilization methods. Other commonly used sterilization processes include low-temperature gas such as ethylene oxide (ETO), liquid chemicals, and hydrogen peroxide gas plasma.

Disinfection

Disinfection is defined broadly as the destruction of microorganisms, except bacterial spores, on inanimate objects (e.g., medical devices such as endoscopes). Three levels of disinfection are achievable depending on the amount and kind of microbial killing involved. These levels of disinfection are as follows:

• 1.

  High-level disinfection (HLD): the destruction of all viruses, vegetative bacteria, fungi, mycobacterium, and some, but not all, bacterial spores. For LCGs, HLD is operationally defined as the ability to kill 10 ⁶ mycobacteria (a six-log reduction). The efficacy of HLD is dependent on several factors and includes the type and level of microbial contamination; effective precleaning of the endoscope; presence of biofilm; physical properties of the object; concentration, temperature, pH, and exposure time to the germicide; and drying after rinsing to avoid diluting the disinfectant.

• 2.

  Intermediate-level disinfection: the destruction of all mycobacteria, vegetative bacteria, fungal spores, and some nonlipid viruses, but not bacterial spores.

• 3.

  Low-level disinfection: a process that can kill most bacteria (except mycobacteria or bacterial spores), most viruses (except some nonlipid viruses), and some fungi.

Although this categorization for disinfection levels generally remains valid, there are examples of disinfection issues with prions, viruses, mycobacteria, and protozoa that challenge these definitions.

Antiseptics are chemicals intended to reduce or destroy microorganisms on living tissue (e.g., skin), as opposed to disinfectants, which are used on inanimate objects (e.g., medical devices such as endoscopes). The difference in the way the same chemical is used to achieve different levels of disinfection and sterilization is important for endoscopy because the contact times for sterilization with any given LCG are generally much longer (hours) than for high-level disinfection (minutes) and may be detrimental to the endoscope. The relative resistance of various microorganisms to LCGs is shown in Box 4.1 .

Spaulding Classification

More than 40 years ago, Earle H. Spaulding developed a rational approach to disinfection and sterilization of medical equipment based on the risk of infection involved with the use of these instruments. The classification scheme defined these categories of medical devices and their associated level of disinfection as follows:

• 1.

  Critical: critical devices or instruments come into contact with sterile tissue or the vascular system. These devices confer a high risk for infection if they are contaminated. This category includes biopsy forceps, sphincterotomes, surgical instruments, and implants, when used in sterile anatomic locations. Reprocessing of these instruments requires sterilization.

• 2.

  Semicritical: semicritical devices contact intact mucous membranes and do not ordinarily penetrate sterile tissue. These instruments include endoscopes, bronchoscopes, transesophageal echocardiography probes, and anesthesia equipment. Reprocessing of these instruments requires a minimum of HLD.

• 3.

  Noncritical: noncritical devices contact intact skin (e.g., stethoscopes or blood pressure cuffs). These items should be cleaned by low-level disinfection.

Endoscopes

GI endoscopes are considered semicritical devices, and the resultant minimal standard for reprocessing is HLD. This standard is endorsed by governmental agencies including the Joint Commission (JC), the Centers for Disease Control and Prevention (CDC), and the FDA. It is also endorsed by gastroenterology societies such as the American Society for Gastrointestinal Endoscopy (ASGE), American College of Gastroenterology (ACG), and American Gastroenterological Association (AGA), as well as medical organizations, including the Association of Perioperative Registered Nurses (AORN), Society of Gastroenterology Nurses and Associates (SGNA), Association for Professionals in Infection Control and Epidemiology (APIC), and American Society for Testing and Materials (ASTM). HLD of endoscopes eliminates all viable microorganisms, but not necessarily all bacterial spores. Although spores are more resistant to HLD than other bacteria and viruses, they are likely to be killed when endoscopes undergo thorough manual cleaning. In addition, survival of small numbers of bacterial spores with HLD is considered acceptable because the intact mucosa of the GI tract is resistant to bacterial spore infection.

Endoscope sterilization, as opposed to HLD, is not required for “standard” GI endoscopy, as a reprocessing endpoint of sterilization has not been demonstrated to further reduce the risk of infectious pathogen transmission from endoscopes. Sterilization of endoscopes is indicated when they are used as “critical” medical devices, such as intraoperative endoscopy when there is potential for contamination of an open surgical field. In addition, individual institutional policies may dictate sterilization of duodenoscopes and linear endoscopic ultrasound instruments due to elevator mechanisms that have been difficult to clean and eradicate all bacterial contaminants with HLD alone (see the later section on Duodenoscope-Related Infections ).

Despite the complex internal design ( Fig. 4.1 ) of endoscopes, HLD is not difficult to achieve with rigorous adherence to currently accepted reprocessing guidelines. Endoscope features that challenge the reprocessing procedures include:

• Complex endoscope design with several long, narrow internal channels and bends that make it difficult to remove all organic debris and microorganisms (e.g., elevator channel and elevator lever cavity of duodenoscopes).

• A large variety of endoscope vendors and models require different cleaning procedures and devices and materials.

• Occult damage (e.g., scratches, crevices) to the endoscope can sequester microorganisms and promote biofilm formation.

Accessories

All valves, caps, connectors, and flushing tubes need to be adequately cleaned, rinsed, and disinfected or sterilized at the same time the patient-used endoscope is being reprocessed. The water bottle used to provide intraprocedural flush solution and its connecting tubing should be sterilized or receive high-level disinfection at least once daily. The water bottle should be filled with sterile water. Because accessory items often do not have unique identification numbers, it is critical to ensure they are dedicated to and stored with the endoscope that they are used with. This is necessary to ensure that if there is an outbreak, it is possible to identify which accessory components were used. This may require the use of disposable accessory holders or holders such as mesh bags that are also reprocessed along with the accessories.

Most accessory instruments used during endoscopy either contact the bloodstream (e.g., biopsy forceps, snares, and sphincterotomes) or enter sterile tissue spaces (e.g., biliary tract) and are classified as critical devices. As such, these devices require sterilization. These accessories may be available as disposable “single-use” or “reusable” instruments. Reuse of devices labeled single-use only remains controversial but has been commonly employed in many practices, primarily for economic benefits. The FDA considers reprocessing a used single-use device into a ready-for-patient-use device as “manufacturing,” and as a result, hospitals or third-party reprocessing companies that reprocess these devices are required to follow the same regulations as the original equipment manufacturers (i.e., obtain 510[k] and premarket approval application; submit adverse event reports; demonstrate sterility and integrity of the reprocessed devices; and implement detailed quality assurance monitoring protocols). This includes the development of standards and policies to determine the maximum number of uses for the devices and the training of staff in the reprocessing procedures. The regulatory burden imposed by these requirements essentially eliminated the practice of the reprocessing of single-use devices by most hospitals.

Automated Endoscope Reprocessors (AERs)

AERs were developed to replace some of the manual disinfection processes and standardize several important reprocessing steps, thereby eliminating the possibility of human error and minimizing exposure of reprocessing department personnel to chemical sterilants. AERs continuously bathe the exterior surface of the endoscope and circulate the LCG under pressure through the endoscope channels. The AER manufacturer identifies each endoscope (brand and model) that is compatible with the AER and specifies limitations of reprocessing models of endoscopes and accessories. Variations in AERs may require customization of the facility design to accommodate requirements for ventilation; water pressure, temperature, and filtration; plumbing; power delivery; and space. All models of AERs have disinfection and rinse cycles. In addition, the AERs may also have one or more of the following automated capabilities:

• 1.

  Some AERs utilize and discard small quantities of LCG per HLD cycle, whereas others have a reservoir of LCG that is reused over multiple cycles. The latter design results in gradual dilution of the LCG and requires intermittent testing to verify maintenance of the minimum effective concentration (MEC). Product-specific test strips need to be used regularly to monitor these solutions, which should be discarded whenever they fall below the MEC or when the use-life expires, whichever comes first.

• 2.

  The temperature and cycle length can be altered to ensure HLD or sterilization based on the LCG and type of endoscope.

• 3.

  The AER should ensure circulation of LCGs through all endoscope channels at an equal pressure with flow sensors for automated detection of channel obstruction.

• 4.

  The AER should be self-disinfecting.

• 5.

  Vapor recovery systems are available.

• 6.

  Low intensity ultrasound waves are an option.

• 7.

  Variable number of endoscopes per cycle.

• 8.

  Some AERs flush the endoscope channels with forced air or with 70% to 80% ethyl or isopropyl alcohol followed by forced air to aid in drying the endoscope channels, thereby eliminating residual water, which reduces microbial growth during storage.

• 9.

  The AER should incorporate a self-contained or external water filtration system.

LCGs and AERs must meet specified performance levels for HLD to receive FDA clearance. This is defined as a reduction in residual organic loads and a 6-log ₁₀ killing of resistant indicator organisms (typically Mycobacterium bovis ). All AERs marketed in the United States meet these criteria. The ASGE has published a summary of vendor-specific AERs and their compatible LCGs. The FDA has approved labeling some AERs as washer-disinfectors due to the introduction of automated, brushless washing of endoscope channels prior to the disinfection cycle. Utilization of this AER washing cycle provides an extra margin of safety by providing redundancy of cleaning; however, the existing multisociety guideline and other international standards emphasize that manual cleaning is still necessary when a washer-disinfector is used to assure the overall efficacy of HLD.

One AER (Steris System 1E [SS1E]; Steris Corp, Mentor, OH) has received FDA approval for liquid chemical sterilization, as opposed to HLD, for heat-sensitive devices that cannot be sterilized by traditional means. This system uses filtered, ultraviolet-treated water that enters the AER and mixes with a peracetic acid-based formulation that is subsequently heated to 46°C to 55°C for liquid chemical sterilization. This system is designed for “point of use” sterilization, as sterile storage is not possible. For flexible endoscopes processed through the SS1E, there is still a requirement for an alcohol rinse and drying prior to placing the endoscope into a storage cabinet.

The FDA also requested that AER manufacturers conduct additional validation testing to evaluate AER reprocessing effectiveness with regard to the recess around the duodenoscope's elevator lever area. An FDA communiqué released in February 2016 indicated that validation testing on three AER models (Advantage Plus [Medivators; Minneapolis, MN], DSD Edge [Medivators], and System IE [Steris Corp]) was complete and adequate. In November 2015, the FDA issued a recall under consent decree for all Custom Ultrasonics (Ivyland, PA) AERs because of the company's inability to validate that their AERs were able to adequately wash and disinfect duodenoscopes to mitigate the risk of patient infection. In a subsequent safety communication, the FDA recommended that health care facilities should not use Custom Ultrasonics System 83 Plus AERs for reprocessing duodenoscopes and should transition to alternative methods for duodenoscope reprocessing.

Liquid Chemical Germicides and Sterilization Technologies

LCGs have inherent limitations; however, they are universally used to reprocess flexible endoscopes and accessories due to their relative convenience, safety, and rapid action. LCGs used as HLDs should ideally have the following properties: broad antimicrobial spectrum, rapid onset of action, activity in the presence of organic material, lack of toxicity for patients and endoscopy personnel, long reuse life, low cost, odorless, ability to monitor concentration, and nondamaging to the endoscope or the environment. HLD solutions can act as sterilants if an increased exposure time is used ; however, the exposure time required to achieve sterilization with most LCG solutions is far longer than is practical, and therefore these formulations are only used for HLD.

The efficacy of chemical disinfectants and sterilants is dependent on their physical properties including concentration and temperature; the length of exposure of the endoscope to the chemical solutions; the type and amount of microbial debris on the endoscope; and the mechanical components of the endoscope such as channels and crevices. Because the chemicals are toxic to humans and the environment, proper handling, thorough rinsing, and appropriate disposal are essential for human safety. When selecting a HLD product, institutional requirements need to be taken into consideration with important variables including the number of endoscopes processed per day, training requirements, turnaround time, cost information, and regulatory issues regarding safe use of the HLD products. Health care workers who use HLDs need to be familiar with and have readily accessible, product/brand-specific Material Safety Data Sheets (MSDS) and keep current with regulatory changes and new product developments. Users should consult with manufacturers of endoscopes and AERs for compatibility before selecting an LCG. The most commonly used FDA approved LCGs for disinfection of flexible endoscopes include glutaraldehyde, ortho-phthalaldehyde (OPA), peracetic acid, and hydrogen peroxide ( Table 4.1 ) based chemicals in varying combinations and concentrations. Some formulations contain combinations of microbicidal agents, including glutaraldehyde and phenol/phenate, peracetic acid and hydrogen peroxide, and glutaraldehyde and isopropyl alcohol. The FDA periodically updates a list of approved HLD solutions along with some of their attributes, such as contact time and temperature required for HLD.

Sterilization of endoscopes is indicated on occasions when they are used as critical medical devices during open surgical procedures. The risk for contamination of the operative field exists when a nonsterile endoscope enters the abdomen through an incision, as occurs with selected methods of intraoperative enteroscopy or postsurgical anatomy endoscopic retrograde cholangiopancreatography (ERCP).

Endoscopes, when sterilized, require low-temperature methods because they are heat labile and therefore, unlike most other medical or surgical devices, they cannot undergo steam sterilization. ETO is the most commonly employed low-temperature sterilization process and a valuable method of sterilizing flexible endoscopes. However, a lengthy aeration time is required following ETO sterilization to allow desorption of all residual toxic gas from the endoscope. Additional steps must be taken, such as the application of a venting valve or the removal of the water-resistant cap to ensure proper perfusion with the gas and to prevent damage to the endoscope due to excessive pressure build-up. In addition, there are potential hazards to staff, patients, and the environment related to ETO toxicities ( Table 4.2 ). The International Agency for Research on Cancer has classified ETO as a known (group 1) human carcinogen. Within the past two decades, several new, low-temperature (< 60°C) sterilization systems have been developed, including hydrogen peroxide gas plasma, vaporized hydrogen peroxide, peracetic acid immersion, and ozone (see Table 4.2 ).