Listen Up! Bacteria Commonly Found on Physician Stethoscopes

The humble stethoscope carried by physicians and other professionals in the intensive care unit (ICU) is laden with a wide range of bacteria, including bacteria known to cause infections acquired in hospitals, according to a new molecular analysis of stethoscope contamination.

Even after physicians cleaned the devices with alcohol swabs, hydrogen peroxide wipes, or bleach, the stethoscopes still weren’t fully decontaminated, say researchers.

Nonetheless, senior investigator Ronald Collman, MD (University of Pennsylvania Perelman School of Medicine, Philadelphia), said that other than Staphylococcus, which was found on every personal and single-use stethoscope, and was also highly abundant, most of the other bacteria identified as “the known bad actors” weren’t present in very high quantities.

“The number one thing that contaminated the stethoscopes were the types of normal bacteria found in people that aren’t pathogens, that don’t cause disease,” Collman told TCTMD. “Normal nonpathogenic bacteria dominated the communities, but within that we did find DNA sequences from bacteria that are associated with healthcare infections.”

Systematic cleaning really did reduce the abundance of bacteria. It didn’t in all cases get it down to a sparkling, clean stethoscope, but it did reduce it. Ronald Collman

In their paper published December 12, 2018, in Infection Control & Hospital Epidemiology, lead investigator Vincent Knecht, MD (University of Pennsylvania Perelman School of Medicine), and colleagues point out that stethoscopes have been previously “implicated as vectors for nosocomial transfer of bacteria” that are linked with infections acquired in the healthcare setting. Several culture-based studies have identified stethoscopes contaminated with pathogens, such as methicillin-resistant and -sensitive Staphylococcus spp, multidrug-resistant P. aeruginosa, and Streptococcus spp, among others.

Healthcare professionals don’t help things either, with multiple studies showing they infrequently clean their stethoscopes between patients.

Using bacterial rRNA gene deep sequencing, analysis, and quantification, the researchers profiled the entire bacterial population on 20 stethoscopes collected from physicians, nurses, and respiratory therapists in the ICU at the Hospital of the University of Pennsylvania and 20 single-use disposable stethoscopes used in patient rooms. They also profiled 10 unused single-use disposable stethoscopes as a control arm.

“In the last number of years, a whole range of new methods have been introduced to understand microbial communities,” said Collman. “These are sequence-based methods, molecular methods, or molecular tracking, which were developed in the broader field of microbial ecology, but what has really driven the research in the last decade is the human microbiome. So we can use sequence-based methods to understand the composition of microbial communities, particularly bacteria.”

Culture-based studies are limited to bacteria of a priori interest, whereas molecular analysis is not, added Collman. At his institute, there are several research groups using deep gene-sequencing to understand the microbial ecology of the hospital environment and to get a better handle on infection control.            

One limitation of the deep-sequencing method is that it uses DNA to identify bacteria and as such is unable to determine if the bacteria is living or dead. It can also have difficulty “pinpointing the species of bacteria,” said Collman. “For example, [Staphylococcus] is one of the major things we found, and for about half of the stethoscopes we could say it was [S. aureus], which is the more concerning member of the Staph genus. For many of the other bacteria we found, we could only identify it to the level of the genus, not the species.”

Other pathogens identified included Pseudomonas, Acinetobacter, Clostridium, Enterococcus, Stenotrophomonas, and Burkolderia. Although these pathogens frequently showed up on stethoscopes, their relative abundance was quite rare. 

As part of the study, the stethoscopes were returned to the physicians, nurses, and therapists and they were asked to clean them using the method they would normally use between patients. Most used hydrogen peroxide swipes, but alcohol swabs and bleach wipes were also used. Cleaning the stethoscopes reduced the amount of bacteria, but the devices were still not as clean as the unused single-use stethoscopes that served as the control arm.

“Systematic cleaning really did reduce the abundance of bacteria,” said Collman. “It didn’t in all cases get it down to a sparkling, clean stethoscope, but it did reduce it.” The bottom line, he said, is that physicians and healthcare professionals need to “be absolutely rigorous in adhering to infection control procedures, and that includes maximally decontaminating stethoscopes.” At Penn, the healthcare team in the ICU relies on the single-use disposable stethoscopes. “We throw them out,” he said. “We don’t use them on a second patient.”