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ICU Stethoscopes Harbor DNA from Nosocomial Bacteria (CME/CE)


Action Points

  • Researchers using molecular assays found communities of bacteria on practitioners’ stethoscopes, including those implicated in nosocomial infections.
  • Note that cleaning using common methods appeared to reduce bacterial levels but did not eliminate them.
  • Note that the study methods could not distinguish between live and dead bacteria, nor identify antibiotic-resistant strains.

CME Author: Vicki Brower

Study Authors: Vincent R. Knecht, John E. McGinnis, et al.

Target Audience and Goal Statement:

ICU physicians, nurses, and other healthcare professionals, infectious disease specialists, and internists

The goal is to understand the potential risk that stethoscopes used in ICUs, including those cleaned by a number of different methods, may still harbor bacteria linked to nosocomial infections.

Questions Addressed by this Study:

Stethoscopes are often used on multiple patients, and have been considered as vectors for hospital-based bacterial contamination. In this study, the authors used molecular methods to investigate the bacterial status of stethoscopes used in medical ICUs, even those that are used only once, and whether conventional methods of cleaning stethoscopes effectively decontaminate them and, if not, what microbes may be found on them.

Study Synopsis and Perspective:

Senior investigator Ronald Collman, MD, and colleagues at the University of Pennsylvania (UPenn) Perelman School of Medicine in Philadelphia performed a series of molecular tests on sets of stethoscopes, both single-use and reusable instruments, to determine whether they were contaminated with bacteria and whether standard cleaning methods were effective in removing the microorganisms.

Unique to this study is the method of detecting bacterial contamination: the use of deep-sequencing molecular analysis to analyze practitioners’ stethoscopes. Researchers noted that previous culture-based studies on the role of stethoscopes as potential vectors for the nosocomial transfer of bacteria responsible for healthcare-associated infections were “limited.” Such studies, they wrote, could only identify “agents of a priori interest, but not entire microbial communities,” unlike next-generation sequencing technology they used.

The use of molecular analysis, however, was also an important limitation. While these methods “can provide unbiased profiling of entire bacterial communities in a manner that is both comprehensive and highly quantitative,” Collman and colleagues acknowledged, they cannot distinguish between live versus dead bacteria.

The investigators found evidence of colonies of the following bacteria linked to hospital-associated infections on stethoscopes carried by healthcare professionals in the ICU: Staphylococcus (including S. aureus), Pseudomonas, Acinetobacter, Clostridium, Enterococcus, Stenotrophomonas, and Burkholderia.

Cleaning the stethoscopes using a number of recommended methods had only a modest effect on removing the amount of bacteria detected in this manner on stethoscopes.

In particular, the UPenn researchers swabbed stethoscopes from their hospital’s medical ICU, and used molecular sequencing to analyze the collected samples. These included 10 single-use disposable stethoscopes straight out of the box (clean stethoscopes), 20 single-use disposable stethoscopes being used in inpatient rooms (patient room stethoscopes), 20 stethoscopes carried by physicians, nurses, and respiratory therapists (practitioner stethoscopes), and a set of background controls comprising swabs moistened with saline.

All 40 in-use stethoscopes had a high abundance of Staphylococcus bacteria, with “definitive” S. aureus bacteria present on 24 of 40 stethoscopes tested. While cleaning the stethoscopes reduced the amount of bacterial DNA it did not completely bring all stethoscopes in use in the ICU to the level of “clean,” the authors wrote in Infection Control & Hospital Epidemiology, the journal of the Society for Healthcare Epidemiology of America.

To examine the efficacy of cleaning methods in reducing the presence of bacteria on the stethoscopes, researchers also sampled 10 additional practitioner stethoscopes cleaned with the “standardized cleaning method”: a hydrogen peroxide wipe for 60 seconds and then swabbed when dry.

A third test looked at an additional 20 practitioner stethoscopes, which were swabbed pre-cleaning, then returned to the practitioner who was told to clean it “using the method they usually would use to clean it between patients.” These methods included hydrogen peroxide wipes, alcohol swabs, or bleach wipes, with duration of cleaning based on practitioner preference, the authors said.

Patient-room stethoscopes are typically used for only a single patient, whereas practitioner stethoscopes are used on multiple patients, which raises the possibility of microbial transfer, researchers noted. However, patient-room stethoscopes still showed the presence of significantly higher bacterial concentrations than the clean stethoscopes. Both practitioner and patient-room stethoscopes were significantly higher in bacteria than background controls, whereas clean stethoscopes were indistinguishable from the background controls. All groups of stethoscopes were contaminated in contrast to the background controls, with no difference between patient-room and clean stethoscopes.

Notably, the research did not document actual infection transmission from the devices or quantify the risk of transferring bacteria, nor did it analyze the scopes for viral or fungal contamination.

Source Reference: Infection Control and Hospital Epidemiology, Dec. 12, 2018; DOI: 10.1017/ice.2018.319

Study Highlights: Explanation of Findings

Bacterial DNA was found on stethoscopes in this study in a medical ICU included those originating from the skin, gut, and mouth.

In their paper, authors noted that Staphylococcus was “ubiquitous” on 40 of 40 stethoscopes tested, and represented 6.8% to 14% “of all bacterial sequences, depending on stethoscope set and target region queried.” In addition to Staphylococcus, they also found smaller concentrations of other bacteria linked to healthcare-associated infections on most stethoscopes, such as Pseudomonas and Acinetobacter. About 50% of stethoscopes had Enterococcus, Stenotrophomonas, and Clostridium, and less frequently, Burkholderia bacteria. Practitioner and patient-room stethoscopes’ bacterial samples were characterized by these plus additional bacteria, including Porphyromonas, Bacteroides, Granulicatella, Actinomyces, Prevotella, Streptococcus, Corynebacterium, and Propionibacterium, which are common oral, skin, and gut bacteria.

When comparing the cleaning methods, standardized cleaning reduced the presence of bacteria to a “clean” level in five of 10 examined stethoscopes, while the practitioner method only achieved the same result in two of 10 stethoscopes.

Bacterial contamination was greatest on practitioner (personal) stethoscopes, followed by patient-room stethoscopes, whereas never-used “clean” stethoscopes were not distinguishable from background controls. Researchers found that the bacterial communities were “complex.” Molecular analysis revealed that the communities detected on clinician and patient-room stethoscopes were indistinguishable, and significantly different from clean stethoscopes and control instruments. Commonly used cleaning techniques were “only partially successful at modifying or eliminating these communities,” researchers wrote. Cleaning reduced but did not eliminate contamination to the level of clean stethoscopes nor did it substantially change the overall makeup of the bacterial communities found, they wrote.

“This study underscores the importance of adhering to rigorous infection control procedures, including fully adhering to CDC-recommended decontamination procedures between patients, or using single-patient-use stethoscopes kept in each patient’s room,” Collman said in a statement.

An important question raised by researchers is what quantity of bacteria on a stethoscope is sufficient to cause infection? That remains to be determined, they wrote.

The CDC, in its guidelines for disinfection, state that “medical equipment surfaces” such as stethoscopes should be disinfected with an EPA-registered low- or intermediate-level disinfectant. These guidelines added that “use of a disinfectant will provide antimicrobial activity that is likely to be achieved with minimal additional cost or work.” The authors noted in their conclusion that these recommended cleaning methods were apparently not routinely followed.

In addition to being unable to distinguish between dead versus living bacteria, the molecular methods could not identify drug-resistant strains of the bacteria either, the investigators acknowledged.

“Useful future directions would be to use these molecular approaches to identify improved cleaning methods, enhance species-level identification of pathogens, quantify live versus dead bacteria, and define fungal and viral contaminants… [and] shotgun metagenomic sequencing would be useful to analyze drug-resistance genes that might be carried between patients on practitioner stethoscopes,” they concluded.

Original MedPage Today story by Molly Walker.

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