This article discusses concerns about the re-contamination of flexible endoscopes with opportunistic, waterborne microorganisms, including Pseudomonas aeruginosa, following their immersion in a high-level disinfectant or liquid chemical sterilant, which is a common practice prior to the flexible endoscope’s clinical use.

April 3, 2013 — During the past decade, lapses in the proper reprocessing of reusable medical equipment have been published in the media. Investors Business Daily, for instance, published on its front page, in February, 2000, an article that discussed multiple patient injuries caused by bronchoscopes contaminated with P. aeruginosa. (This outbreak is discussed in detail in another blog by Dr. Muscarella entitled “Did the CDC get it Right?“; click here to read it.)

Recommendations that Dr. Muscarella provide to prevent infections associated with improperly reprocessed  reusable medical equipment may be read by clicking here.

The incidence of infections of P. aeruginosa linked to contaminated gastrointestinal (GI) endoscopes, and even more frequently, to bronchoscopes – such as the bacterial outbreak following bronchoscopies that this aforementioned article in Investors Business Daily discusses – in the 1980’s, 1990’s and the early part of this century, compared to that of the past few years, underscores an important point not often discussed:

  • that, if the reduction in the number of reported cases of P. aeruginosa infections linked to contaminated flexible endoscopes over the past decade or two is a reliable demonstration of improvements in infection control, then the effectiveness of specific measures designed to prevent the transmission of this insidious bacterium, like that of other waterborne, opportunistic bacteria, at least via a contaminated GI endoscope or bronchoscope, would appear to have been verified.

These specific measures include:

  1. the use of bacterial filters to improve the quality of the water used to rinse flexible endoscopes;
  2. terminal drying of the flexible endoscope’s internal channels, in addition to before storage, between patient procedures; and
  3. storage of the flexible endoscope in accordance with published guidelines (e.g., with its distal tip hanging freely in a well-ventilated, clean environment, as opposed to being stored in a damp suitcase).

But let’s get back to a discussion of outbreaks of P. aeruginosa and related topics that was the focus of the aforementioned Investors Business Daily newspaper article.

More background

Microorganisms responsible for causing healthcare-acquired infections (HAIs) are either endogenous or exogenous.  The patient’s own microbial flora contain many different types of endogenous microorganisms. When, for example, those that are indigenous to the gut are transferred by a surgical instrument to the patient’s respiratory tract, a HAI may result.[1] Most surgical wound infections are caused by endogenous microorganisms.[2]

In contrast, exogenous microorganisms reside in the outside environment and when introduced into the patient may cause healthcare-associated infection. Examples include environmental microorganisms on contaminated medical instruments.

Pseudomonas: P. aeruginosa, which is a gram-negative bacillus (rod-shaped) that is commonly found in soil and other natural environments, has been reported to cause many different types of true- and pseudo-outbreaks,3-6  including those of pneumonia, bacteremia,[3] and cholangitis.[7] Although P. aeruginosa ordinarily does not cause disease in healthy individuals, it is an opportunistic microorganism that can pose a serious risk to patients with compromised immune systems.

Click here to read Dr. Muscarella’s blog that discusses the differences between a true- and pseudo-infection or outbreak of bacteria.

Requiring little more than a moist environment to colonize and proliferate, P. aeruginosa can survive exposure to very adverse conditions.8 Respiratory equipment, pressure monitoring devices, and other exogenous sources, including whirlpools, sinks, and tap water,[3,9-13] have been linked to outbreaks of P. aeruginosa.

Flexible endoscopes

Reports have also linked gastrointestinal endoscopes to P. aeruginosa infection.[3,7] One study reported an outbreak of gram-negative bacteremia following endoscopic retrograde cholangiopancreatography (ERCP).[3] Even though filtered to yield “sterile” water, the tap water, which recontaminated the endoscope with P. aeruginosa during rinsing, was identified as a source of this outbreak. Improving the quality of the rinse water is important, as healthcare-associated infections linked to contaminated tap water may be more common than reported.[13]

Click here to read an abstract of Dr. Muscarella’s peer-reviewed, featured editorial in Endoscopy entitled  “Investigation and prevention of infectious outbreaks during endoscopic retrograde cholangiopancreatography” (or ERCP).

The importance of a 70% alcohol rinse, forced-air drying

The contribution of the cleaning and high-level disinfection of flexible endoscopes to the prevention of patient infection is well established.[14]

But, if there were one measure alone that has reduced the risk of infection by a flexible endoscope, it would arguably be the adopted practice of drying its internal channels (refer to the aforementioned Investor’s Business Daily article). Indeed, the significance of endoscope drying to the prevention of HAIs and outbreaks linked to P. aeruginosa and other waterborne microorganisms requires revisiting and re-emphasis. The internal channels of inadequately dried endoscopes provide an  ideal environment for the colonization and growth of opportunistic bacteria.[3,4,15]

The importance of endoscope drying to the prevention of infections of P. aeruginosa and other waterborne microorganisms requires re-emphasis.

In one report, five of seven patients, each of whom was the first patient of the day, died from P. aeruginosa (serotype 10) septicaemia following ERCP.[7] A similar report documented patient infection and death linked to endoscopes contaminated with P. aeruginosa.[4] And investigation of a pseudo-epidemic of Legionella pneumophila found that the tap water used to rinse bronchoscopes after chemical immersion was the source of the contamination.[16]

Click here to read Dr. Muscarella’s blog “Outbreak of Legionnaires’ Disease at a Veterans Administration Medical Center.”

Only after the endoscope was thoroughly dried using a 70% alcohol rinse, followed by forced air, was each of these outbreaks terminated. Notably, failure to thoroughly dry each of the endoscope’s internal channels can yield a catastrophic outcome.[3-7]

Water filtration systems

More and more health care facilities are using automated flexible endoscope reprocessors (AERs), which are designed to reprocess flexible endoscopes between patient procedures. One salient advantage of AERs, compared to manual reprocessing, is the ease with which they can be connected to a water filtration system, which includes a 0.1 or 0.2 micron filter, to yield bacterial-free rinse water. For their part, bacterial filters can improve significantly the quality of the rinse water.

But bacterial water filters can also fail, and over the course of their use-life, may allow bacteria and other microbial debris to pass through their membrane and recontaminate the endoscope during water rinsing.[3,18-20]

Therefore, to protect the patient from a water filter failing in clinical practice,[3,18-20] drying the endoscope is essential.[21] Proper maintenance and replacement of the filters and their housing are necessary to improve their effectiveness and reliability.[16,19] Although expensive and not routinely performed, more frequent microbiologic sampling of the medical facility’’s rinse water may be necessary to ensure its quality meets certain minimum specifications (eg, < 200 CFUs/ml).

To read an abstract of Dr. Muscarella’s peer-reviewed article “Application of environmental sampling to flexible endoscope reprocessing: the importance of monitoring the rinse water,” click here.

Room for improvement

Published reports and guidelines recommend rinsing the endoscope’s channels with 70% alcohol, followed by forced air drying.[3-5,21] Although this recommendation is usually heeded when tap water is used for rinsing,[3,17,21] it may not be as readily practiced if the endoscope is rinsed with filtered water labeled as bacterial-free or sterile.

The need for federal regulatory agencies, standards committees, and professional endoscopy and infection control organizations to recommend flushing the endoscope with 70% alcohol, followed by forced-air drying, both before storage and after each patient procedure, and whether the endoscope is rinsed with tap or filtered water, has been stressed through the years by Dr. Muscarella.

To read Dr. Muscarella’s significant peer-reviewed article “Inconsistencies in Endoscope-Reprocessing and Infection-Control Guidelines: The Importance of Endoscope Drying,” click here.

What is ‘sterile’ water?

In truth, lacking in the medical literature is a clear description of the parameters of bona fide “sterile” water, how it is produced, and how it compares to and differs from other types of water, such as: (a) bottled, sterile water, (b) filtered water labeled as sterile or as bacterial-free, and (c) tap water.

Such comparisons and distinctions between water types may not be trivial. For example, guidelines for preventing healthcare-associated pneumonia recommend rinsing bronchoscopes with sterile water (MMWR January 03, 1997;46[RR-1];1-79). Discussions that address the significance of these recommendations, their intent, and what other types of water may be adequate for rinsing bronchoscopes are necessary.

Issues related to endoscope storage also warrant further discussion. If the endoscope will not be used for a day or two, the importance of terminally rinsing the endoscope with 70% alcohol, followed by forced air-drying, is clear and cannot be overstated. But what if a reprocessed (and wet) endoscope is to be stored for only a few hours: is complete drying still necessary? (“Storage” refers not only to a location but also to a period of idle time.) And if not, how much time (if any) can elapse between patient procedures before complete drying the endoscope becomes necessary? The answers to these questions have important infection control implications.

And, further, what if the endoscope were properly reprocessed, dried, and stored, for how long may it remain in storage before it would have to be reprocessed before its next use?

Click here to read Dr. Muscarella’s blog “An event-related paradigm applied to the storage of flexible endoscopes,” which responds to this question.

Whereas drying the endoscope’s channels before storage is essential to the prevention of HAIs, the importance of performing this practice between patient procedures is less clear, as data in its support is limited. Nevertheless, because even low numbers of P. aeruginosa and other opportunistic bacteria can pose serious infection in immuno-compromised patients, drying the endoscope between patient procedures is a prudent practice.

Notably, the Society of Gastroenterology Nurses and Associates (SGNA) recommends drying GI endoscopes, both between patient procedures and before storage, no matter the quality of the rinse water.


The internal channels of flexible endoscopes provide an ideal environment for the colonization and growth of P. aeruginosa. To all but eliminate the risk of transmitting opportunistic microorganisms to the patient via an endoscope, rinsing the endoscope’s channels with 70% alcohol, followed by forced-air drying, is recommended: (a) before storage and, (b) when feasible, between patient procedures. Further, this practice of drying the endoscope is important to perform, whether the endoscope is rinsed with tap water or water filtered through a 0.2 micron bacterial membrane.

Finally, discussions that examine under what conditions (if any) disinfecting endoscopes before the first patient of the day may be appropriate seem timely and are also encouraged,[22] lest an inadequately dried endoscope be stored wet the previous day and result in patient infection.

Article by Lawrence F Muscarella, PhD, posted 4/3/2013; updated 4/4/2013.

References available upon request.

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