AAMI ST91: Flexible and Semi-Rigid Endoscope Processing Compared with Canadian Guidance

Stainless steel ultrasonic cleaning tank with a removable mesh basket used for instrument cleaning
Stainless steel ultrasonic cleaning tank with a removable mesh basket used for instrument cleaning

A flexible endoscope is the only instrument in a reprocessing room that can be destroyed by the cleaning step meant to protect it. Its outer sheath is a sealed polymer jacket, its working channel is a long narrow lumen that a brush has to reach, and its elevator and valves are moving parts that trap soil. That combination is why flexible and semi-rigid endoscope processing has its own standard in the United States, ANSI/AAMI ST91, rather than being folded into the general instrument guidance, and why the Canadian federal guideline for flexible endoscopy reads as a document about a separate discipline.

This article sets out what ST91 covers, walks the processing chain step by step, and places each step next to the Canadian source that governs it — the Public Health Agency of Canada's guideline for flexible gastrointestinal endoscopy and flexible bronchoscopy, and Public Health Ontario's provincial guidance on cleaning, disinfection and sterilization. It concentrates on the two steps that fail first in practice: leak testing and manual brushing. Nothing here replaces the endoscope manufacturer's instructions for use, which govern the device-specific detail in every case.

Quick facts

  • ANSI/AAMI ST91 covers flexible and semi-rigid endoscope processing and is titled Flexible and semi-rigid endoscope processing in health care facilities. It was approved by AAMI on 1 October 2021 and by ANSI on 21 December 2021, and has been reaffirmed as ST91:2021/(R)2026.
  • Its scope runs across point of use treatment, transporting, leak testing, cleaning, packaging, high-level disinfecting and/or sterilizing, storage, and quality control for flexible GI, bronchoscopy, ear, nose and throat, and urology endoscopes, and other reusable flexible and semi-rigid endoscopes.
  • The Canadian federal guideline states that "there are some bronchoscopes that can be steam sterilized but most flexible endoscopes require low temperatures for disinfection/sterilization".
  • Public Health Ontario's provincial guidance classifies fibre-optic and video endoscopes of the hollow viscera as semicritical and requires a minimum of high-level disinfection before use.
  • ST91 is a United States standard. Neither the American standard nor the Canadian federal guideline is a statute; in Canada the statutory device layer is the Medical Devices Regulations, and provincial guidance supplies the practice requirements.
  • Leak testing is the step with the clearest written protection: an endoscope that fails the dry leak test should not go on to the immersion leak test.

Why endoscope reprocessing is its own chain

The Spaulding classification places a flexible endoscope entering a hollow viscus in the semicritical group, which sets the minimum at high-level disinfection rather than sterilization. Two exceptions matter in practice. Endoscopes that enter sterile cavities, such as bronchoscopes and cystoscopes, are preferred to be sterilized, and where the instrument is not compatible with sterilization the minimum is again high-level disinfection. Accessories that break the mucosal barrier, such as biopsy forceps, are critical items and must be sterile, which for reusable biopsy forceps means steam sterilization rather than chemical processing.

The Canadian federal guideline's position on why the chain is long is stated directly: the instruments are difficult to disinfect and easy to damage because of their intricate design, including narrow long lumens and delicate materials. Public Health Ontario reaches the same conclusion from the other direction, noting that flexible fibre-optic and video endoscopes require special cleaning and handling because of the complexity of their design.

The practical consequence is that the reprocessing sequence is fixed and each step has a failure mode that the next step cannot repair. Soil left in a channel is not removed by a disinfectant. Moisture left in a channel becomes the growth medium for the organisms that survive storage.

The processing chain, step by step

Table 1 walks the chain in the order ST91 presents it, with the Canadian requirement alongside each step. The ST91 column gives the section topic as published in the standard's section structure; the Canadian column quotes the governing document.

Step AAMI ST91 section topic Canadian requirement alongside it
Point of use treatment Point of use treatment, replacing the older term precleaning; procedure steps listed as a to k Flush and wipe the endoscope at point of use with a soft lint-free cloth or endoscope sponge, using a freshly prepared enzymatic cleaning solution, then place it and its accessories in a covered leak-proof container for transport (PHO provincial guidance)
Transport of the contaminated scope Transport of contaminated endoscopes The endoscope should be transported to the reprocessing area in an enclosed container, and contaminated and clean endoscopes are not transported in the same container at the same time (PHAC guideline)
Leak testing Manual (dry) leak testing; wet leak testing Pressure and leak testing should be performed according to the manufacturer's instructions after each use and before immersion in the reprocessing solution; an instrument that fails the leak test is removed from clinical use and repaired (PHAC guideline). Provincial guidance adds that a scope failing the dry leak test should not undergo the immersion leak test
Manual cleaning and brushing Cleaning general considerations; manual cleaning The endoscope and its disassembled components are immersed in freshly prepared enzymatic detergent, and all accessible channels are flushed and brushed to remove organic and other residues (PHAC guideline)
High-level disinfection or sterilization High-level disinfection; manual processing procedure; automated endoscope reprocessor features Semicritical endoscopes receive a minimum of high-level disinfection after each use, using a sterilant or high-level disinfectant that carries a Health Canada drug identification number (PHAC guideline; PHO provincial guidance)
Rinsing and drying Manual drying After disinfection the scope is rinsed and the channels flushed, an alcohol rinse is used where tap water is used, and the channels are dried with forced medical grade air before storage (PHAC guideline)
Storage Storage; endoscope drying cabinets; maximum safe storage time; endoscope storage risk assessment Endoscopes are stored uncoiled, hanging vertically in a clean, dry, ventilated area that prevents recontamination or damage, with valves detached, dried and stored separately (PHAC guideline)
Quality control Quality control general considerations; product identification and traceability Records include the results of each inspection and, for endoscopes, each leak test (PHO provincial guidance)

Two structural differences between the two systems are visible in that table. ST91 names the first step "point of use treatment" rather than precleaning, and it treats automated reprocessor features, drying, storage and quality control as sections of the standard rather than as afterthoughts. The Canadian documents reach the same content through a federal guideline plus provincial guidance rather than through a single process standard.

Leak testing: the step that protects the scope

Leak testing exists to find a breach in the outer sheath before liquid reaches the optics and the interior electronics. It is a device-protection step before it is anything else, and the two guidance systems treat it consistently.

The Canadian federal guideline's recommendation is to perform pressure and leak testing according to the manufacturer's instructions after each use and before immersion of the endoscope in the reprocessing solution, and to remove any instrument that fails the test from clinical use for repair. Public Health Ontario's provincial guidance goes a step further on sequencing: the patency and integrity of the endoscope sheath is verified through leak testing performed before and during immersion, an endoscope that fails the dry leak test should not undergo the immersion leak test, and the results of each leak test are part of the record.

ST91 carries manual dry leak testing and wet leak testing as named section topics and requires that detachable parts be removed before the dry test. The comparison that matters for a facility writing a procedure is not which document is stricter but where the protection sits: the dry test happens before any liquid is introduced, so a scope that fails it never reaches the immersion tank in the first place.

Table 2 sets out what each test is for and what a failure obliges.

Test What it detects What a failure obliges Source of the rule
Dry leak test Breach in the outer sheath before the scope is wetted Do not proceed to immersion; remove from clinical use and repair PHAC guideline; provincial guidance adds the dry-before-wet ordering
Wet leak test Breach that becomes apparent only under immersion pressure Remove from clinical use; do not continue the cycle PHAC guideline
Post-repair return to use Whether the repaired scope is intact Re-enter the normal leak-test step of the chain Manufacturer instructions; PHAC guideline framework

Why manual brushing is the step that fails

Every published account of endoscope-related infection points at the cleaning stage rather than at the disinfectant. The Canadian federal guideline records a historical list of reprocessing errors associated with transmission, and the items on it are procedural: failure to perform leak testing before cleaning, failure to clean suction channels with a brush, inadequate drying time before storage, and replacement of the valves on the endoscope before storage.

The federal guideline's cleaning recommendations are correspondingly specific. All accessible channels should be flushed and brushed to remove organic and other residues, with the valves repeatedly actuated during cleaning to reach each surface. Cleaning brushes should match the size of the channel or port so that the bristles contact the surfaces; disposable cleaning items are preferred, and reusable cleaning items must be cleaned, inspected for damage and given at least high-level disinfection after each use, and discarded if worn or damaged. The external surfaces are cleaned with a soft lint-free cloth, sponge or brushes, and enzymatic detergent is discarded after each use because it is not microbicidal.

The federal agency's 2016 advisory on duodenoscope-related infections states the same conclusion in one sentence: outbreaks associated with flexible endoscopy have usually, though not always, been associated with breaks in the cleaning or disinfection stage of reprocessing. That is the reason a facility can hold a fully validated high-level disinfectant and still have a reprocessing problem.

Where the two systems diverge

Table 3 places the two guidance systems side by side on the points a facility procedure has to resolve.

Question AAMI ST91 (United States) Canadian guidance
Legal status A voluntary consensus standard, not a statute A federal guideline (PHAC) plus provincial guidance (for example PHO/PIDAC in Ontario); the statutory device layer is the Medical Devices Regulations
Instrument scope Flexible and semi-rigid endoscopes, including flexible GI, bronchoscopy, ear, nose and throat and urology endoscopes The Canadian federal guideline addresses flexible gastrointestinal endoscopy and flexible bronchoscopy
Minimum for a semicritical scope High-level disinfection or sterilization, as the standard sets out Minimum of high-level disinfection before use for semicritical endoscopes; sterilization preferred for bronchoscopes and cystoscopes where the device allows it
Disinfectant selection Process defined by the standard, with the device manufacturer's instructions controlling compatibility A sterilant or high-level disinfectant that carries a Health Canada drug identification number
Storage before reprocessing is needed Maximum safe storage time is a defined section, with a risk-assessment approach A defined maximum storage time is stated for the endoscope; the storage area is cleaned on a recurring schedule with an approved low-level disinfectant or cleaner
Training and competency Certification and competency requirements are emphasised Competency testing of personnel reprocessing endoscopes is performed at least annually and documented; staff do not reprocess endoscopes until competency is established
Record content Product identification and traceability section Results of each inspection and, for endoscopes, each leak test

The divergence that most often surprises a Canadian reader is the disinfectant column. A high-level disinfectant sold in Canada is a drug product, and the federal guideline's requirement is written in those terms: the sterilant or high-level disinfectant used should be one that carries a Health Canada drug identification number. A product that is compliant in another market is not automatically usable in Canada.

What changes at the purchasing step

A reprocessing programme is built from three purchases, and they are usually made in the wrong order. The endoscopes and their instructions for use come first, because the manufacturer determines which chemistries are compatible and what the leak-test procedure is. The cleaning step comes second, because it is the step that decides whether the disinfection step has anything to work on. The monitoring and record layer comes third.

That makes the cleaning bench the procurement item worth specifying carefully. A benchtop dual-frequency ultrasonic cleaner handles the immersion cleaning of the small parts and accessories that surround an endoscope, while the large-channel work stays manual. The chemistry that goes with it is an enzymatic ultrasonic cleaning solution concentrate, used freshly prepared and discarded after each use as the federal guideline requires, with a plain 6.5 L ultrasonic cleaner available where a larger tank is needed. Case quantities run through the wholesale account page.

Accessories that penetrate the mucosal barrier, such as reusable biopsy forceps, follow the other route: they are steam sterilized after cleaning rather than chemically processed, which puts them back into steam-cycle monitoring. Where a facility is setting up that monitoring, a biological indicator trial pack is a low-commitment way to test a steam-monitoring format against the workflow before ordering case quantities. A facility building the paperwork around that bench can print the record sheet from the compliance log centre — four record groups covering twenty fields, presented in the form's own wording so that an inspector comparing paper to form sees the same terms in the same order — and generate a dated page there without an account or sign-up. Where a facility wants its own leak-test and record procedure compared against the federal and provincial text, that comparison can be requested rather than assumed.

Have a question about your own facility? Send it in and you will get a written answer specific to your setup, with the regulation or standard it is based on cited. Ask your compliance question.

Flexible endoscope reprocessing adds a long paper trail to the sterilizer log. Clinics can run a free, sector-specific self-check that walks through the sterilization records and checks an inspector is most likely to look for — about two minutes, prints as a checklist, and needs no account.

Related reading

CliniEco enzymatic ultrasonic cleaning solution concentrate used in the manual cleaning step of instrument reprocessing

Frequently Asked Questions

Is AAMI ST91 a legal requirement in Canada?

No. ST91 is a United States consensus standard published by the Association for the Advancement of Medical Instrumentation, and it is a voluntary standard. In Canada the federal guideline and provincial guidance supply the practice requirements, and the statutory layer for the device itself is the Medical Devices Regulations.

What is the difference between a dry leak test and a wet leak test?

The dry leak test is run before the scope is wetted and is intended to detect a breach in the outer sheath before any liquid can reach the interior. The wet leak test is run during immersion. Provincial guidance states that an endoscope failing the dry leak test should not go on to the immersion leak test, because the dry failure has already answered the question.

Why does the endoscope need a brush and not just a flushing cycle?

Because the federal guideline requires all accessible channels to be flushed and brushed to remove organic and other residues, with brushes sized so that the bristles contact the channel or port surfaces. Flushing alone moves fluid; the brush is what removes adherent debris from the channel wall.

How long can a processed endoscope be stored before it must be reprocessed?

The Canadian federal guideline states a defined maximum storage time for the processed endoscope. Because storage conditions, the cabinet in use and the facility's own risk assessment all bear on the answer, the storage interval and the conditions attached to it should be taken from the governing documents alongside the endoscope and cabinet manufacturer's instructions rather than from a general rule of thumb.

Does the disinfectant have to be registered in Canada?

Yes. The federal guideline's recommendation is that the sterilant or high-level disinfectant used should be one that carries a Health Canada drug identification number, which is the drug-product layer. It sits separately from the device compatibility question.

What records does endoscope reprocessing have to produce?

Provincial guidance includes the results of each inspection and, for endoscopes, each leak test among the records to be kept. ST91 carries product identification and traceability as its own section, and quality control as a general consideration, which is the same requirement approached from the process side.

Where do the manufacturer's instructions fit against the standard?

They control. Both the federal guideline and provincial guidance direct the facility to the endoscope manufacturer's instructions for leak testing, cleaning and product compatibility, and the standard is applied through those instructions rather than instead of them.

CliniEco Medical holds Medical Device Establishment Licence MDEL #35334. This article compares published standard and guidance content and does not make a disinfection or sterilization performance claim for any product.

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