Tests show DNA from many species, even after washing DNA from an abundance of bacteria linked to healthcare-associated infections, including Staphylococcus, was found on stethoscopes carried by healthcare professionals in the ICU, and cleaning only led to a modest reduction, researchers found. On a set of 40 stethoscopes in use in an ICU, all 40 had a high abundance of Staphylococcus DNA, with "definitive" S. aureus DNA present on 24 of 40 stethoscopes tested, reported Ronald G. Collman, MD, of the University of Pennsylvania (UPenn) Perelman School of Medicine in Philadelphia, and colleagues. Moreover, 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. However, the DNA-based analysis could not determine whether living bacteria were present, and the study did not document actual infection transmission from the devices or quantify the risk of it. Collman and colleagues said previous culture-based studies on the role of stethoscopes as vectors for nosocomial transfer of bacteria responsible for healthcare-associated infections were "limited." Such studies could only identify "agents of a priori interest, but not entire microbial communities," unlike next-generation sequencing technology. The UPenn researchers swabbed stethoscopes from their hospital's medical ICU, using molecular sequencing to analyze the collected samples. These included 10 single-use disposable stethoscopes straight out of the box (control set), 20 single-use disposable stethoscopes being used in inpatient rooms (patient room stethoscopes), and 20 stethoscopes carried by physicians, nurses, and respiratory therapists (practitioner stethoscopes). To examine the impact of cleaning methods, researchers 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 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. The authors noted that Staphylococcus DNA was "ubiquitous" on stethoscopes, and represented about 7% 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 bacterial DNA linked to healthcare-associated infections, such as Pseudomonas and Acinetobacter. When comparing the cleaning methods, standardized cleaning reduced bacterial DNA levels to a "clean" level in five of 10 examined stethoscopes, while the practitioner method only achieved the same result in two of 10 stethoscopes. "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. 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, with these guidelines adding that "use of a disinfectant will provide antimicrobial activity that is likely to be achieved with minimal additional cost or work." A study limitation was that the DNA-based methods could not identify drug-resistant strains. "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. Source
