The Wet Scope: How Drying and Storage Failures Undo a Disinfected Endoscope

When a hospital defends a scope-infection claim, the first document it usually produces is a disinfection record: the automated reprocessor ran its cycle, the cycle passed, the scope was released. That record is real, and it is often accurate. It is also answering only half the question. A flexible endoscope is a bundle of narrow, meters-long channels, and the disinfectant that travels through them is a liquid. What happens to the water left behind after the last rinse determines whether a scope that was genuinely clean at 4:00 p.m. is still clean when it goes into the next patient the following morning.

Why Does Moisture Inside a Scope Matter?

Because water is what the relevant bacteria need to multiply. The organisms most often implicated in endoscope-associated infections are waterborne, gram-negative species — Pseudomonas aeruginosa, Klebsiella pneumoniae, Stenotrophomonas maltophilia. High-level disinfection kills organisms at the moment the chemical contacts them. It does not sterilize the channel against anything that arrives afterward, and it confers no protection during storage. A droplet of retained fluid, plus the residual organic material and the hours a scope spends hanging in a cabinet, is a small incubator.

The longer-term problem is biofilm. Once bacteria in standing water attach to a channel wall and secrete a protective matrix, they become dramatically harder to remove or kill, and subsequent disinfection cycles may not reach them. A narrative review published in Gastrointestinal Endoscopy examining the impact of wet storage on biofilm formation and contamination of patient-ready endoscopes treated moisture during storage as a recognized driver of that process. This is also why drying failures compound: a scope stored wet repeatedly does not simply carry yesterday's risk forward, it can build a reservoir that survives the very process meant to eliminate it.

What the Drying Studies Actually Found

Two published studies frame this issue better than any general description, and they land in very different places — which is the point.

In 2018, Cori Ofstead and colleagues published a multisite study in the American Journal of Infection Control titled “Residual moisture and waterborne pathogens inside flexible endoscopes.” The researchers examined 45 endoscopes across three hospitals. They found retained fluid inside 49% of them, and microbial growth in samples from 71%. Retained fluid was associated with higher ATP levels and with microbial growth; organisms recovered included Stenotrophomonas maltophilia and Citrobacter freundii. Critically, the authors reported that reprocessing and drying practices conformed with guidelines at one site and were substandard at the other two — the variable was not the technology, it was the practice.

In 2024, a real-world study on drying effectiveness in the same journal produced a number that deserves to be quoted precisely. Investigators assessed 42 endoscopes (22 gastroscopes and 20 colonoscopes) using droplet-detection cards, visual inspection of connectors and distal ends, and borescope examination of the interiors. After the automated endoscope reprocessor completed its default alcohol flush and air purge cycles — the steps many facilities treat as the drying step — 100% (42 of 42) of the endoscopes were still wet. After a dedicated 10-minute forced-air drying cycle, 100% were dry. Substantial fluid emerged from the distal ends within the first 15 seconds of that cycle.

Read those together and the practical conclusion is uncomfortable but clear: a reprocessor cycle that completed successfully, alcohol flush and air purge included, tells you almost nothing about whether the scope was dry. The disinfection record and the drying question are separate inquiries.

What Does the National Standard Require?

ANSI/AAMI ST91:2021 is the U.S. national standard for flexible and semi-rigid endoscope processing, and its 2021 revision tightened the drying and storage provisions considerably. It recommends actively drying endoscope channels with pressure-regulated forced instrument air or HEPA-filtered air, delivered into the lumens through a direct channel connection, for at least 10 minutes. The emphasis on forced air into each channel is deliberate. Hanging a scope vertically and letting gravity drain it is a widespread practice and an ineffective one; as the infection-prevention literature has noted, the channels are simply too narrow for fluid to run out on its own.

The standard also draws a line most patients have never heard of, between two things that look identical from the hallway:

• Drying cabinets circulate HEPA-filtered or instrument air through the cabinet and through each individual endoscope channel at continuous positive pressure. They actively dry the inside of the scope during storage.
• Conventional storage cabinets circulate filtered air through the cabinet space at positive pressure but push no air through the channels. They protect the outside of a scope. They do not dry the inside.

Under ST91:2021, endoscopes hung in a cabinet without channel-drying capability must be dried before storage, and cabinets belong in a secure clean workroom rather than in the procedure room. A hospital that bought conventional cabinets and treats them as if they were drying cabinets has a gap between the equipment it owns and the outcome it assumes.

How Long Can a Scope Sit Before It Must Be Reprocessed?

There is no fixed national answer, and that absence is itself important. ST91:2021 acknowledges that the point at which a stored, processed scope should no longer be considered patient-ready — the “hang time” — has not been well defined by the evidence. Rather than setting a universal maximum, the standard directs each facility to conduct a documented multidisciplinary risk assessment, weighing a list of considerations, and to set its own policy on that basis. In practice, facilities have landed in different places; published quality-improvement work in AAMI's Biomedical Instrumentation & Technology describes one hospital extending hang time from 7 days to 14 after completing such an assessment.

For a patient, the takeaway is not that a particular number is right or wrong. It is that a facility's own written policy and its own risk assessment become the benchmark it is measured against. A hospital that set a 7-day limit and used a scope on day 11, or that never performed the risk assessment the standard calls for before adopting a longer window, has a documentation problem that does not depend on second-guessing the science.

Why Drying Is the Least-Documented Step in Reprocessing

Disinfection is machine-driven and self-documenting. An automated endoscope reprocessor runs a validated cycle and prints a record with a time stamp, and that printout is easy to produce in litigation. Drying, by contrast, is frequently a manual step performed by a technician, timed by hand or by habit, with no automatic log at all. The 10-minute forced-air requirement is exactly the kind of task that quietly compresses when the schedule is full and a scope is needed in the next room.

That asymmetry is why the drying question is so often left unexamined. The records a hospital volunteers first are the ones that document the step it can prove. Establishing what happened after the cycle ended requires asking for a different set of documents — and knowing they exist.

A Trial Lawyer’s Read

“When the defense hands me a stack of reprocessor printouts, my first thought isn’t that they’re hiding something — it’s that they’ve answered a question I didn’t ask,” says Alex Alvarez, Managing Partner of The Alvarez Law Firm and a Board Certified Civil Trial Lawyer. “A passing cycle is one step. The published data shows scopes coming out of that cycle still wet. So I want the next set of documents: what is your written drying protocol, what equipment performs it, are your storage cabinets drying cabinets or plain cabinets, what is your hang-time policy, and where is the risk assessment behind it? Those aren’t gotcha questions. They’re what the standard itself tells a hospital to have. If liability is established in a case like this, it’s usually established by the gap between the policy on the shelf and the practice in the room.”

The clinical side has to line up with the paperwork. “What I look for is coherence between the organism and the mechanism,” notes Herb Borroto, M.D., J.D., the firm’s Medical-Legal Expert, who holds both a medical degree and a law degree. “If a patient grows a waterborne gram-negative organism — Pseudomonas, Klebsiella, Stenotrophomonas — after an endoscopic procedure, retained moisture is one of the mechanisms that fits, and it’s one I can test against the record. I look at the scope-tracking log, the interval between reprocessing and use, the storage equipment, and the culture results. Sometimes the records support the connection. Sometimes they rule it out, and I say so. The value of the drying-and-storage inquiry is that it’s answerable from documents rather than from speculation.”

The Records That Answer the Question

If drying and storage are at issue, these are the categories that matter — and they sit apart from the disinfection file:

• Automated endoscope reprocessor cycle printouts and logs, including which alcohol flush and air purge options were enabled.
• The facility’s written drying protocol, and the equipment used to perform forced-air drying.
• Purchase, installation, and service records for storage cabinets — establishing whether they are drying cabinets or conventional cabinets.
• The written hang-time policy, plus the multidisciplinary risk assessment ST91:2021 calls for in setting it.
• Scope-tracking logs showing the interval between reprocessing and the next patient use of that specific device.
• Sterile processing technician training, competency, and staffing records for the relevant shift.
• Borescope inspection findings and any microbiological surveillance culture results.

These records are kept on limited retention schedules, and some are overwritten or discarded on a rolling basis. Our guide to requesting and preserving hospital records covers how a preservation demand works and why timing drives what survives. Drying and storage also sit alongside the two related failure points we have written about separately: the quality of the final rinse water, and the broader framework of hospital reprocessing negligence.

What to Do Now

If you or a family member developed a serious infection — a bloodstream infection, sepsis, or a drug-resistant organism — in the days or weeks after a colonoscopy, ERCP, cystoscopy, or bronchoscopy, a hospital’s assurance that the scope was properly cleaned is not the end of the inquiry. Whether it was properly dried and stored is a separate question with its own separate paper trail. Our guide to the signs a scope caused an infection can help you recognize the timing and symptoms worth taking seriously.

A short, no-obligation review can tell you whether the facts warrant pulling those records and whether a filing deadline may be approaching. We represent patients nationwide. Free case review. No Fees Unless We Recover Money for You.

Frequently Asked Questions

Can a wet endoscope cause an infection?

Yes. Residual moisture left inside an endoscope’s narrow internal channels after cleaning gives waterborne, gram-negative bacteria such as Pseudomonas aeruginosa, Klebsiella pneumoniae, and Stenotrophomonas maltophilia the water they need to multiply during storage and to build biofilm on channel walls. A 2018 multisite study published in the American Journal of Infection Control examined 45 endoscopes at three hospitals and found retained fluid in 49% of them and microbial growth in samples from 71%, with retained fluid associated with higher contamination. High-level disinfection kills organisms at the moment it is applied; it does not prevent regrowth in a scope that is put away wet. That is why drying is treated as part of reprocessing rather than an optional finishing touch.

How long should an endoscope be dried before storage?

ANSI/AAMI ST91:2021, the U.S. national standard for flexible endoscope processing, recommends actively drying the internal channels with pressure-regulated forced instrument air or HEPA-filtered air delivered into the lumens through a direct channel connection for at least 10 minutes. The standard emphasizes forced air directed into each channel rather than passive air-drying or hanging the scope and relying on gravity, because endoscope channels are too narrow for fluid to drain out on its own. Alcohol flush and air purge cycles built into an automated endoscope reprocessor are not, by themselves, treated as sufficient drying under the standard.

Does storing an endoscope in a cabinet make it safe?

It depends entirely on which kind of cabinet. ANSI/AAMI ST91:2021 distinguishes drying cabinets, which push HEPA-filtered or instrument air through each individual endoscope channel at continuous positive pressure, from conventional storage cabinets, which circulate filtered air through the cabinet space but not through the channels. A conventional cabinet keeps the outside of a scope clean and protected; it does not dry the inside. Under the standard, endoscopes hung in a cabinet without channel-drying capability must already be dried before they go in. A scope stored wet in a conventional cabinet is a scope stored wet.

What records show whether a scope was properly dried and stored?

Several categories of hospital records bear directly on drying and storage, and they are usually separate from the disinfection records a facility produces first. They include automated endoscope reprocessor cycle printouts and logs, the facility’s written drying protocol and the equipment used to perform it, purchase and service records showing whether storage cabinets are drying cabinets or conventional cabinets, the written hang-time policy and the multidisciplinary risk assessment ST91:2021 calls for in setting it, scope-tracking logs showing the interval between reprocessing and the next patient use, technician training and competency files, and any borescope inspection or microbiological surveillance results. These records are kept on limited retention schedules, which is why identifying and preserving them early matters.

Sources

• Ofstead CL, et al. — “Residual moisture and waterborne pathogens inside flexible endoscopes: Evidence from a multisite study of endoscope drying effectiveness,” American Journal of Infection Control (June 2018) (45 endoscopes at three hospitals; retained fluid in 49%; microbial growth in samples from 71%; Stenotrophomonas maltophilia and Citrobacter freundii recovered; drying practices substandard at two of three sites). ajicjournal.org
• “Fluid retention in endoscopes: A real-world study on drying effectiveness,” American Journal of Infection Control (2024) (42 endoscopes — 22 gastroscopes, 20 colonoscopes; 100% still wet after default automated endoscope reprocessor alcohol flush and air purge cycles; 100% dry after a 10-minute forced-air drying cycle; droplet cards, visual inspection, and borescope assessment). ajicjournal.org
• ANSI/AAMI ST91:2021 — Flexible and semi-rigid endoscope processing in health care facilities (minimum 10 minutes of pressure-regulated forced instrument or HEPA-filtered air into channels via direct connection; distinction between drying cabinets and conventional storage cabinets; requirement to dry before storage in non-drying cabinets; cabinet location in the clean workroom; hang time not well defined, multidisciplinary risk assessment recommended). aami.org
• “Using a Risk Assessment to Transition to a 14-Day Endoscope Hang Time,” Biomedical Instrumentation & Technology (AAMI) (facility extending hang time from 7 to 14 days following a risk assessment aligned with ANSI/AAMI ST91:2021). array.aami.org
• “Impact of wet storage and other factors on biofilm formation and contamination of patient-ready endoscopes: a narrative review,” Gastrointestinal Endoscopy (moisture during storage as a driver of bacterial proliferation and biofilm formation). giejournal.org
• “Endoscope drying and its pitfalls,” Journal of Hospital Infection (2017) (limitations of passive drying and gravity drainage in narrow endoscope channels; alcohol flush followed by forced-air drying). journalofhospitalinfection.com
• “Sterilization Central: Drying and Storage of Flexible Endoscopes: An Area of Growing Concern,” Biomedical Instrumentation & Technology (AAMI, 2020) (drying and storage as an under-addressed stage of endoscope reprocessing). array.aami.org
• U.S. Food & Drug Administration — “Infections Associated with Reprocessed Duodenoscopes” (reusable flexible endoscopes can remain contaminated after reprocessing performed according to the manufacturer’s instructions). fda.gov

This article is for general informational purposes only and is not legal or medical advice. It summarizes published peer-reviewed studies, national processing standards, and regulatory statements as of the publication date; standards and scientific findings can change, and this article does not describe the outcome of any client’s case. References to reprocessing practices, published research, and standards describe general findings, not any individual’s claim, and the existence of a drying or storage deficiency at any facility studied is not evidence about any other facility. Nothing here creates an attorney-client relationship, and no result is promised or implied. Past results do not guarantee future outcomes. Deadlines and legal standards vary by state and by the facts of each case. If you believe you may have a claim, consult a licensed attorney promptly.