January 3, 2013 (updated July 28, 2013, revised April 24, 2014) — This article responds to an article published in The Los Angeles Times. Although this Times’ article was published in 2003, its discussion about the potential risk of infection following colonoscopy remains as timely and germane today as it was almost a decade ago.  This article by Lawrence F Muscarella, PhD, is based on a more detailed article that can be read by clicking here.


In its February 13, 2003, issue, The Los Angeles Times published an article that discussed the risk of disease transmission during colonoscopy,(1) a procedure that uses a colonoscope to exam and treat diseases of the colon (and rectum). The likely impetus for this newspaper article’s publication was in part the issuance of a letter of concern written by the California Department of Health Services (CDHS) to over 1000 general acute care hospitals.(1-3)

Dated January 8, 2003, this letter discusses the importance of properly cleaning and disinfecting flexible endoscopes after each use.(2)

This letter also recommends that hospital administrative staff — in addition to developing and implementing policies and procedures to ensure that the facility’s endoscope reprocessing practices are in accordance with the manufacturer’s instructions — monitor the cleaning and (high-level) disinfection of endoscopes as part of the facility’s quality assurance program.

Colonoscopes are long and narrow flexible fiber-optic or video endoscopes that feature several internal channels used, among other functions, to suction patient debris and to wash the colon’s mucosa as required to enhance examination and visualization.

Additionally, colonoscopes and most other types of flexible endoscopes, such as bronchoscopes and gastroscopes, feature an internal instrument channel through which a biopsy forceps (or other accessory) can be passed to sample and remove for analysis a patient’s potentially abnormal or diseased tissue.

The CDHS promptly issued this letter after it received reports from two hospitals that observed patient debris leaking from a colonoscope just prior to its use on a patient.(3)  Reprocessing staff at these two hospitals apparently were unaware that certain models of colonoscopes feature an “auxiliary water” channel that requires cleaning and disinfection.

As a result, this channel, which had become contaminated during routine use, remained contaminated after reprocessing, posing a potential risk of disease transmission.(1-3)

Although identified more than a decade, these two hospitals’ reports of improper reprocessing of colonoscopes are not unlike other, similar ones reported more recently.

A Veterans Administration medical center (VAMC) in Miami (FL) in 2009, for example, identified patient debris in the auxiliary water channel of colonoscopes that had been “reprocessed” and were presumed, incorrectly, to be safe for reuse. More about this Miami VAMC’s breach can be read in two other of Dr. Muscarella’s blogs (article #1 and article #2).

Out of concern for the potential risk of cross-infection associated with improperly reprocessed endoscopes, these two hospitals contacted more than 3000 patients who had undergone colonoscopy and were deemed at risk.(1,3)

These patients were advised to be evaluated to determine whether they might have been infected during colonoscopy with a potential pathogen, such as the hepatitis C virus (HCV).

As of the May, 27,2003, none of these “at risk” patients had reported an infection(4) (a finding that ostensibly suggests the risk of disease transmission during colonoscopy is quite low, The Los Angeles Times article’s reporting notwithstanding).

Also concerned about patient safety at these two and at other hospitals, an endoscope manufacturer (Olympus) mailed a safety notice, dated February 10, 2003, to an additional 2200 hospitals in the United States to remind users that, although rarely linked to cross-infection, a colonoscope can transmit disease if all of its channels, ports and connectors are not properly reprocessed after each use.(1,5)

Emphasis in this manufacturer’s safety notice was placed on the importance of cleaning and disinfecting all of the colonoscope’s channels — including the auxiliary water jet channel of specific colonoscope models — even if the channel is not used during the procedure.(5)

The identification of feces (or another type of patient debris or fluid) on a colonoscope may indicate, among other lapses, the failure to have accounted for and to have reprocessed this lower GI endoscope’s auxiliary water channel. Click here to read about this same topic in another of Dr. Muscarella’s articles entitled “A Legal Case about Improperly Reprocessed Flexible Endoscopes.” 

Questionable reporting

Several salient issues were discussed in this Los Angeles Times article, including the importance of endoscope reprocessing to the prevention of cross-infection, and of colonoscopy as a crucial screening tool for colon cancer,(1) the second-leading cause of cancer-related deaths in the U.S.(6)

Although tens of thousands of patients die each year in the U.S. from colon cancer, this disease has a high cure rate if detected early during a procedure such as colonoscopy.(7)

Reports suggest that as many as 15 million procedures that use a flexible endoscope are performed each year in the U.S.(1,8)  Of this number, it is estimated that approximately 10 million are gastrointestinal (GI) endoscopic procedures,(8) with 4.4 million being colonoscopy.(9)

Because colonoscopy is used so frequently to screen and treat patients for colorectal cancer and other bowel diseases, risks and complications associated with this procedure would have significant and far-reaching public health implications and consequences.

Despite discussing the importance of endoscope reprocessing and colonoscopy, this Los Angeles Times article unfortunately presented a perspective arguably intended less to educate a concerned and vulnerable public than to incite its readership’s understandable fear of disease. Some aspects of its reporting were questionable and not based on fact.

For instance, this newspaper article discusses a recent case in which several patients who underwent GI endoscopy at a clinic in Brooklyn (NY) were infected with the HCV.(1,10)

Although acknowledging that health officials “suspect” that the reuse of contaminated needles was responsible for this HCV outbreak, this Los Angeles Times article reported that “others say the clinic’s failure to sterilize biopsy forceps or properly clean the scopes was the (sic) more likely the cause of the outbreak.”(1)

Click here to read an abstract of Dr. Muscarella’s peer-reviewed article about this Brooklyn GI endoscopy clinic.

This statement (i.e., that “others say the clinic’s failure to sterilize biopsy forceps or properly clean the scopes was the (sic) more likely the cause of the outbreak”)(1) is confusing. In February (2002), a year before the publication of this Los Angeles Times article, the New York City Department of Health (NYCDH) concluded that “the endoscopy itself was not the source of the transmission” of the HCV.(11)

And, as reported by Newsday in an article dated July 3, 2002, the NYCDH concluded last year that this HCV outbreak was a result of the violation of aseptic technique by the clinic’s anesthesiologist — specifically, the reuse of needles and the contamination of multi-dose medicine vials with HCV during the administration of intravenous medications as had been required for patient comfort and sedation.(11,12)

Further, there are no published reports in the medical literature that indicate anything other than the reuse of contaminated needles or another violation of aseptic technique was likely the cause of this HCV outbreak. Who these “others” are that reportedly claim a contaminated GI endoscope or biopsy forceps was more likely responsible for this outbreak is unclear and was not disclosed in the article.

Click here to read another of Dr. Muscarella’s article – written, in part, in reply to a recent article published on the front page of USA Today – that discusses the risk of disease transmission associated with the reuse of contaminated needles and other violations of aseptic technique while administering medications during GI endoscopy and other medical procedures.

Presumably as a consequence of this Brooklyn clinic’s HCV outbreak and the questionable suggestion by “others” that its likely cause was improperly reprocessed endoscopes or biopsy forceps, this Los Angeles Times article reported that New York legislators had decided to study whether toughening the state’s “disinfectant standards for endoscopes” might be warranted.(1)

In truth, these legislators’ sudden and piqued interest with the state’s current standards for endoscope reprocessing probably has little if anything to do with this clinic’s HCV outbreak.

More likely the impetus for debate among these legislators is the publication of emotionally-laced newspaper and magazine articles intended to rouse hysteria (rather than allay fear),(1,13-15) as well as a conspicuous marketing effort to promote the application of various sterilization technologies to flexible endoscopy, notwithstanding the lack of data demonstrating not only that a flexible endoscope can be reliably sterilized using any method, but also that high-level disinfection poses an infection risk.(15,16)

Click here to read the article “Current issues in endoscope reprocessing and infection control during gastrointestinal endoscopy” by Douglas Nelson, M.D. and Lawrence F. Muscarella, Ph.D.

Second, this Los Angeles Times article discusses an isolated and anecdotal report about a patient who claims to have been infected by a colonoscope contaminated with the human papilloma virus (HPV), an otherwise sexually-transmitted contagion.(1)

Discussion of this case in this newspaper’s article is inexplicable and suspect, since a review of the medical literature demonstrates that there are no published reports that document either this specific patient’s case or any other case of the transmission of HPV during colonoscopy or any other GI endoscopic procedure.

With respect to other viruses of clinical concern, during the past ten years only a few reports document the likely transmission of HCV via a contaminated GI endoscope,(17-20) and none was reported in the U.S. Whereas transmission of the hepatitis B virus (HBV) during GI endoscopy is rarely reported,(11,21) there are no reports that document infection of a patient with the feared HIV during GI endoscopy.

This very low number of cases of transmission of these viruses suggests the risk of being infected by a GI endoscope contaminated with HBV, HCV, HIV, or HPV is extremely remote.

The risk of infection by a contaminated GI endoscope has been reported to be one in 1.8 million.(1,8,17) A recent study indicates that this risk is approximately one in 3 million.(11)

Although the risk of infection during GI endoscopy is very low, it can be reduced even further, and the transmission of all pathogens including HCV prevented, by ensuring that endoscopes are reprocessed in strict accordance with the manufacturer’s recommendations and published guidelines.(11,17,22-25)

Data indicate that published endoscope reprocessing standards and guidelines are adequate, effective and prevent the transmission of all pathogenic microorganisms and viruses that may be encountered in the endoscopic  setting.(11,16,17,25-30)

Every documented case of patient infection linked to a contaminated endoscope reports as its cause a breach in endoscope reprocessing protocol, such as: inadequate cleaning, improper disinfection, or insufficient drying of the endoscope; a defective or recalled device; or failure to sterilize the biopsy forceps.(22,23)

Moreover, during the past few years, the majority of the published reports that document disease transmission during flexible endoscopy has been linked to contaminated bronchoscopes—not colonoscopes or other GI endoscopes as the Los Angeles Times article implies by its sheer focused attention.

And several of these published reports identify bronchoscopes contaminated with Pseudomonas aeruginosa and other waterborne bacteria as the cause of the infections and outbreaks.

Transmission of these exogenous microorganisms during flexible endoscopy often indicates—not inadequate cleaning or improper disinfection—but rather re-contamination of the endoscope during rinsing (after chemical immersion) with water that contains bacteria, followed by insufficient drying of the endoscope’s channels.(31-42)

Failure to thoroughly dry the endoscope after reprocessing using a liquid chemical sterilant can result in disease transmission.(43)

Click here to read a blog by Dr. Muscarella entitled “Case Study: A Contaminated Gastrointestinal Endoscope.”

Approximately 500,000 bronchoscopies are performed each year in the U.S.(8,31) This number (the denominator) is a small percentage (11%) of the number of colonoscopies performed (i.e., 4.4 million).

Because more cases of infections (the numerator) linked to contaminated bronchoscopes have been reported during the past several years than infections linked to contaminated GI endoscopes,(11,31-40) it would appear that the risk of infection associated with bronchoscopy may be significantly higher than GI endoscopy.

Several factors may contribute to this not-too surprising finding.

— First, the lower respiratory tract is ordinarily pristine, and the introduction of bacteria inimical to its health and general condition. In contrast, the GI tract in its normal and healthy state is contaminated with large numbers of many different varieties and species of innocuous bacteria, known as bacterial flora. Introduction of bacteria into the GI tract may therefore not always result in infection.

— Second, a large percentage of bronchoscopies are performed on hospitalized and critically ill patients. Because the immune systems of these patients are often severely compromised, introduction of even a small number of bacteria can have catastrophic consequences. GI endoscopy, on the other hand, is routinely performed on an out-patient basis to screen otherwise healthy patients whose intact immune systems are well-equipped to combat and destroy invading microbes. Read: Box A, below.

By not providing its readers with a meaningful and clinically significant exposé that could have focused on recent investigations and reports of healthare-associated outbreaks caused by contaminated bronchoscopes,(33,36-38) this Los Angeles Times article missed its mark, choosing instead to center its misdirected cross-hairs on colonoscopes and other GI endoscopes, despite these instruments being very rarely linked to disease transmission.(11) — Lawrence F Muscarella, PhD

Box A: Failing again to capitalize on an important opportunity fraught with significant public health implications and lessons, this Los Angeles Times article makes no reference to a 1999 report, documented in the Food and Drug Administration’s MAUDE database and investigated by the CDHS, that describes a P. aeruginosa outbreak that resulted in multiple patient injuries and four patient deaths.[36,37]

This outbreak, remarkably similar to two other outbreaks reported in Flushing, NY,(33) and Pittsburgh, PA,[38] was linked to inadequately dried bronchoscopes contaminated with P aeruginosa after automated reprocessing. And, ironically, this outbreak occurred at a hospital located in Los Angeles, CA, this  newspaper’s hometown.[36]

Although it involved multiple injuries and deaths, neither the Centers for Disease Control and Prevention (CDC) nor the FDA investigated, reported on, or publicly discussed this Los Angeles hospital’s outbreak.

— Third, although it correctly stated that as a result of identifying a bacterial outbreak last year a hospital in Baltimore (MD) warned several hundred patients who had undergone bronchoscopy of their potential exposure to P. aeruginosa,(39,40) this Los Angeles Times article implies that this outbreak (and the other outbreaks it discussed) was, among other causes, a result of inherent problems with the current designs of bronchoscopes and other flexible endoscopes.

According to this newspaper article, an endoscope manufacturer reportedly has been aware of these design problems for years but has refused to fix any of them, choosing instead “to bury its head in the sand.”(1)

Click here to read a blog by Dr. Muscarella entitled “Florida Judge Rules in Favor of Veteran In Colonoscopy, Hepatitis C case.”

In truth, the P. aeruginosa outbreak at this Baltimore hospital was caused — not by an ignored inherent limitation in the design of flexible endoscopes — but by an incidental and unanticipated flaw in the manufacturing of the biopsy port channel housing of several bronchoscope models that were subsequently recalled.(39,40)

In addition, there are no published data to suggest that:

  1. current endoscope reprocessing guidelines are inadequate;(42)
  2. high-level disinfection poses an infection risk in endoscopy;(16) or
  3. this P. aeruginosa outbreak in Baltimore (or any of the newspaper article’s other reported outbreaks) was, as implied by The Los Angeles Times, a consequence of health care staff who, while keeping from the public a “dirty little secret” and employing a “McDonald’s-style” mentality simply “to serve more clients,” knowingly and intentionally provide inferior patient care.(1)

And, finally, this Los Angeles Times article reports that there are some current endoscopes on the U.S. market that feature internal channels that “cannot be disinfected” or presumably cleaned.(1)

It is unclear the specific endoscope models or types to which this article is referring. Discussions with two leading endoscope manufacturers indicate that there are no endoscope models currently on the market that contain internal channels that can become contaminated with patient debris during a procedure, but that cannot be adequately cleaned and disinfected using a detergent and a liquid chemical sterilant (or high-level disinfectant).

Click here to read Dr. Muscarella’s article: “An Event-Related Paradigm Applied to the Storage of Flexible Endoscopes.”

Summary and conclusions

Although at times belied by this Los Angeles Times article’s focus on reports of disease transmission during colonoscopy, only 35 cases of likely or possible infection caused by a contaminated GI endoscope have been reported over the last ten years, despite approximately 10 million GI endoscopic procedures being performed each year.(8,11,15,17)

Of these 35 reported cases of infection following GI endoscopy, disease transmission was suspected or confirmed during colonoscopy in only five cases,(11) yielding a risk of approximately one infection for every 9 million colonoscopies.

The benefits to public health gained by undergoing colonoscopy for the screening and early detection of potentially malignant tissues outweigh this low risk of infection, a conclusion that could have been but was not adequately reported or conveyed in this Los Angeles Times article. —– Lawrence F Muscarella PhD

Moreover, whereas only five cases of infection suspected or confirmed to be caused by contaminated colonoscopes were reported over the last decade, during this same period of time a significantly higher number of cases of nosocomial infection and colonization likely or possibly due to contaminated bronchoscopes was reported,(8,31-40) a finding that suggests bronchoscopy may pose a significantly higher risk of infection than colonoscopy and other GI endoscopic procedures.

The reported higher number of infections following bronchoscopy compared to colonoscopy is even more significant when it is realized that the number of bronchoscopies performed per year (500,000 in the U.S.) is but a small percentage (11%) of the number of colonoscopies performed per year (4,400,000 in the U.S.).

As a result of this finding, newspaper articles and other media reports that discuss the risk of infections associated with flexible endoscopes might serve the public better, and both more effectively and earnestly, if each were to focus attention, not on infections potentially related to colonoscopy, but rather on infections linked to contaminated bronchoscopes, which appear to be more frequently reported.

It is also recommended that these media reports discuss the importance of simple and inexpensive precautionary measures — such as terminally drying the endoscope’s internal channels using a 70% alcohol rinse followed by forced air — whose effectiveness to the prevention of the transmission of bacteria during endoscopy is well documented.(11,41)

Important to note, each reported case of disease transmission during bronchoscopy and GI endoscopy identified as its cause a breach in established instrument reprocessing guidelines and recommended practices.(11,18-21)

Published endoscope reprocessing guidelines for years have been shown to prevent disease transmission during flexible endoscopy,(11,42,43) provided reprocessing staff strictly adhere to the guidelines’ recommended steps, which include cleaning, high-level disinfection, and drying of the endoscope after each use.

Finally, although an otherwise reputable news source, the Los Angeles Times was remiss in its failure to disclose that at least one of the researchers interviewed for its article and presented as an objective contributor has been financially associated with sterilization technologies discussed in the article.(13,44)


Although it did not accurately characterize the very low reported risk of infection associated with colonoscopy, this Los Angeles Times article brings to the public’s attention the importance of colonoscopy as a crucial screening tool for colon cancer.

This newspaper article also provides the public with critical insight into the potential adverse consequences associated with improper endoscope reprocessing, a topic with which the public needs to become more familiar and knowledgeable.

Finally, this newspaper article’s discussion provides the opportunity to review several important infection control recommendations applicable to both GI endoscopy and bronchoscopy.  Review of the health care facility’s policies and procedures for inclusion of these recommendations is suggested:

  1. Develop and implement a written procedure that includes step-by-step instructions for properly reprocessing the endoscope after each use. Ensure all reprocessing steps are in accordance with the endoscope manufacturer’s reprocessing instructions and as required with published endoscope reprocessing guidelines.(43)
    • Note: Different endoscope models can feature unique channels—such as the colonoscope’s water jet channel, or the duodenoscope’s elevator-cable channel, and, unless sealed, these channels will most likely require specialized or additional reprocessing steps. It is therefore important to review the reprocessing instructions, diagrams and schematics of every endoscope model in inventory to ensure each channel is reprocessed even if it is not used during the procedure.(5)
  2. Ensure endoscope reprocessing staff are well-trained and knowledgeable in endoscope design, the principles of infection control, and standard precautions. Periodically conduct competency tests to evaluate the staff’s knowledge of the specific reprocessing instructions and channel adapters required for every endoscope model in inventory. Additional reprocessing training and testing may be required whenever a new endoscope model is introduced into use.
  3. Develop and implement a quality assurance (QA) program that monitors all of the steps of endoscope reprocessing and ensures staff are provided with and properly using all of the required reprocessing equipment (e.g., channel adapters, luer fittings, detergents, liquid chemical sterilants, cleaning brushes). It is recommended that this QA program include not only a surveillance procedure designed to detect and report infections (and pseudo-infections) that could be a result of inadequate endoscope reprocessing, but also a tracking system that permits quick identification of patients on whom a potentially contaminated endoscope was used.(45)
  4. If a bacterial outbreak occurs that is linked to a contaminated endoscope, microbiologically sample as recommended the endoscope and all other potentially contaminated environmental surfaces, such as the rinse water used during endoscope reprocessing. Transmission of waterborne bacteria,whether a strain resistant or susceptible to antibiotics,typically suggests inadequate drying of the endoscope.
  5. Ensure the reprocessing procedure includes terminal drying of the endoscope’s channels using 70% alcohol followed by forced air. Endoscope drying is necessary, particularly for side-viewing duodenoscopes and bronchoscopes, whether the water used to rinse the endoscope is tap water, bacteria-free water, bottled sterile water, or “sterile” filtered water.(42,43)
  6. Consider using endoscopes manufactured by a single manufacturer, to avoid confusion, enhance familiarization with the endoscopes’ reprocessing requirements, and minimize the risk of using improper channel adapters or “irrigators,” connection kits, connectors, fittings, and caps during reprocessing. In general, endoscope manufacturers provide their own unique set of reprocessing instructions.
  7. When using an automated endoscope reprocessor (AER), ensure reprocessing staff understand its operating instructions and have in supply the AER’s specific set of channel adapters required for every endoscope model in inventory. Resolve any conflicts or discrepancies between the reprocessing instructions provided by the AER and endoscope manufacturers.(45)  Consider periodically conducting competency tests to evaluate the staff’s knowledge of the proper operation of the AER and of the specific reprocessing instructions and channel adapters required to connect the AER properly to every endoscope model in inventory. Also, consider using AERs from a single company to minimize the risk of user error.
  8. Leak-test the endoscope in accordance with its manufacturer’s instructions. Also, repair the endoscope as needed, and have the endoscope periodically serviced as recommended.(45) Failure to properly service and maintain an endoscope can result in disease transmission.(31)
  9. Ensure aseptic technique is always practiced during the handling and administration of intravenous (IV) medications. Consider using single-dose IV medication vials. And, use a new sterile syringe and needle (and IV tubing line) for each patient.(10,25,47)
  10. Consider using single-use disposable biopsy forceps and other endoscopic accessories. Clean and steam sterilize all critical reusable instruments not damaged by heat.(25,48-50)  Maintain the sterility of these critical instruments prior to use.  Steam sterilization is recommended because it is reported to be more reliable and effective than low-temperature sterilization processes.(49,50)
  11. Appoint a staff member to remain in close contact with the manufacturer(s) of the endoscopes in inventory (and with the manufacturer of the AER, if used) to learn quickly of device recalls and to resolve any confusing or conflicting endoscope reprocessing instructions.

[Note: An article entitled “Risk of Infection Associated with Endoscopy” by the manufacturer “ASP” can be read by clicking here.]

This article’s references are available by clicking here.

Article by: Lawrence F Muscarella, PhD, posted on 1-3-2013; updated 7-28-2013; revised: 4/24/2014.

3 thoughts on “Risk of Disease Transmission Associated with Gastrointestinal Endoscopy”
  1. Dr Muscarella, I am a supervisor at an SPD that reprocesses 40-50 scopes a day. We are constantly bombarded with questions regarding infection control and disease transmission by our colonoscopies. During my research I came upon your excellently written blog and attempted to access the list of references and unfortunately the link does not seem to be working. Would it be possible to be emailed the reference list? Or possibly have the link sent to my email?
    Thank you

    1. Dear Dane,

      Thank you for your email and interest in my blog. Your comments are appreciated, and it is a pleasure to assist you.

      The references to this article my be read at: http://www.myendosite.com/htmlsite/2003/refs05603.pdf

      Further, in reply to your comment that your department is being “bombarded” with questions, you may consider having its endoscope-reprocessing practices reviewed and audited. When a patient or consumer requests of your department information about infection control and disease transmission during GI endoscopy, you would respond by saying that you had recently had performed an external, independent peer review that substantiated the safety of your department’s practices. Such an audit would contribute to optimizing your practices and to allaying concerns about the risk of disease transmission during colonoscopy. As you may know, I perform audits of medical facilities’ endoscope-reprocessing practices. A brochure of my services is available at: http://www.myendosite.com/literature/Brochure.pdf

      Let me know if I can be of further assistance to you.

      Best regards, Larry
      Lawrence F Muscarella PhD

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