Microbial testing assesses the “bioburden” of an item, which is the total count of bacterial and fungal colony-forming units, or CFUs, per sample.
Microbial testing is used as routine surveillance for pathogens, or in the event of an outbreak. It is performed after endoscope disinfection, sterilization, and drying, and not after manual cleaning like the cleaning verification tests for residual soils or adenosine triphosphate, commonly known as ATP. Because surveillance cultures are performed after endoscope reprocessing has been completed, they can help assess a facility’s reprocessing procedures.
Routine surveillance cultures are not currently part of U.S. reprocessing guidelines but many international organizations advocate for their use. The range of time suggested between surveillance cultures varies widely, from after each use to annually.
The Association of periOperative Registered Nurses, or AORN, and the American National Standards Institute/Association for the Advancement of Medical Instrumentation (ANSI/AAMI) recommend a multidisciplinary team assess the need for surveillance cultures. This team determines the frequency, methods, and benchmarks and should include laboratory staff.
Traditional bacterial cultures can take days to finalize, which of course means the endoscope is out of use, pending the results. The time and expense of cultures, combined with the fact that many facilities do not have laboratories familiar with interpreting these results, has given rise to alternative testing methods and send-out labs.
Determining whether the microorganism to be cultured is a common environmental organism or a human pathogen is the first order of business. The American Society of Microbiology recommends that samples be sent to a lab experienced with this kind of interpretation, as many hospital labs lack the expertise for this kind of testing.
Bacterial culturing can be performed once an organism has been determined to be a human pathogen versus an environmental contaminant. Some pathogens generate more concern than others, and some of the highest-profile outbreaks have been related to duodenoscopes.
The Emergency Care Research Institute (ECRI), an independent group, recommends cultures at least weekly of all duodenoscope channels and elevator mechanisms using culture media specific to the drug-resistant group of bacteria known as carbapenem-resistant Enterobacteriaceae (CRE).
The U.S. Centers for Disease Control and Prevention (CDC) responded to CRE outbreaks from duodenoscopes by developing guidance specific to these types of endoscopes.
The CDC’s protocol for assessing bacterial contamination of duodenoscopes has an algorithm for doing surveillance cultures every 60 endoscopic retrograde cholangiopancreatography (ERCP) procedures, monthly, or after each use. The CDC also says that sampling after each use can be reserved for patients known or suspected to be infected or colonized with multidrug-resistant microorganisms like CRE.
In its duodenoscope sampling protocol, the CDC distinguishes between high- and low-concern microorganisms. High-concern microorganisms are more likely to cause disease if transmitted to a patient. They include:
Low-concern microorganisms are less likely to cause disease. They include:
No matter the concern level, repeated positive contamination results for an endoscope can indicate a damaged instrument that needs to be replaced or assessed by the manufacturer.
Editor’s Note: We’ve hyperlinked throughout this piece to the source materials that guided our research but thought we’d group all of the citations here for you to peruse and explore in more detail if you’d like. Thanks for reading.
Association for the Advancement of Medical Instrumentation (AAMI) with the American National Standards Institute Inc. (ANSI). “ANSI/AAMI ST91:2015: Flexible and semi-rigid endoscope processing in health care facilities.” Association for the Advancement of Medical Instrumentation. Arlington, VA, 2015.
U.S. Centers for Disease Control and Prevention (CDC). “Interim Protocol for Healthcare Facilities Regarding Surveillance for Bacterial Contamination of Duodenoscopes after Reprocessing.” Version 3.11.15.
Petersen et al. “Multisociety guideline on reprocessing flexible GI endoscopes: 2016 update.” Gastrointestinal Endoscopy 2017: 85, No. 2, pp. 282–294.
Association of periOperative Registered Nurses (AORN). “Guideline for Processing Flexible Endoscopes” in Guidelines for Perioperative Practice. Denver, CO, 2016: pp. 675–758.