Researchers also found Staph and other bacteria on stethoscopes after they had been cleaned, leading to scrutiny of cleaning agents and methods

Microbiologists, anatomic pathologists, and clinical laboratory leaders should be intrigued by a university study which found stethoscopes worn by caregivers contained vast amounts of bacteria, including Staphylococcus aureus (Staph), a major cause of hospital-acquired infections (HAIs).

Using next-generation DNA sequencing, University of Pennsylvania Perelman School of Medicine researchers found the deadly bacteria on stethoscopes stored and used in, of all places, an intensive care unit (ICU), where patients are particularly vulnerable to infection.

Even more compelling was the discovery of DNA from the Staph bacteria on the stethoscopes even after they were cleaned. Though the tests could not differentiate between live and dead bacteria, the researchers found other non-Staph bacteria as well, including Pseudomonas and Acinetobacter.

Similar conditions could no doubt be found in most healthcare settings in America, highlighting the critical importance for rigorous cleaning procedures and protocols.

The researchers published their paper in Infection Control and Hospital Epidemiology, the journal of the Society for Healthcare Epidemiology of America (SHEA).

Deadly Bacteria Becoming Harder to Kill

HAIs are becoming increasingly difficult to prevent partly because Staph bacteria, such as Methicillin-resistant Staphylococcus aureus (MRSA), are becoming increasingly resistant to antibiotics, according to the Centers for Disease Control and Prevention (CDC).


“The 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,” said Ronald Collman, MD (above), the study’s senior author and Professor of Medicine, Pulmonary, Allergy, and Critical Care at UPenn’s Perelman School of Medicine, in a news release. (Photo copyright: Penn Medicine.)

The researchers acknowledged that previous culture-based bacterial studies looked at stethoscopes, but noted the results fell short of the view next-generation sequencing technology can offer for identifying bacteria, as well as determining the effectiveness of cleaning chemicals and regiments.

“Culture-based studies, which focus on individual organisms, have implicated stethoscopes as potential vectors of nosocomial bacterial transmission [HAI]. However, the full bacterial communities that contaminate in-use stethoscopes have not been investigated,” they wrote in Infection Control and Hospital Epidemiology.

Study Employs RNA Deep-Sequencing

The UPenn researchers used bacterial 16 ribosomal RNA (16S rRNA gene) deep-sequencing to study the bacteria, Becker’s Healthcare explained.

The stethoscopes analyzed were in-use as follows:

• 20 worn by physicians, nurses, and respiratory therapists;

• 20 single patient-use disposable stethoscopes available in ICU patient rooms; and,

• 10 unused single-use disposable stethoscopes to serve as a control.

All stethoscopes worn and/or used in the ICU were found to be contaminated with abundant amounts of Staphylococcus DNA. “Definitive” amounts of Staph was found by researchers on 24 of 40 tested devices, noted MedPage Today.

“Genera relevant to healthcare-associated infections (HAIs) were common on practitioner stethoscopes, among which Staphylococcus was ubiquitous and had the highest relative abundance (6.8% to 14% of containment bacterial sequences),” the researchers noted in their paper.

Cleaning Methods Also Examined

The researchers also studied the hospital’s cleaning agents and procedures:

• 10 practitioner stethoscopes were examined before and after a standard 60-second cleaning procedure using hydrogen peroxide wipes;

• 20 additional stethoscopes were assessed before and after cleaning by practitioners using alcohol wipes, hydrogen peroxide wipes, or bleach wipes.

All methods reduced bacteria. But not to the levels of a new stethoscope, the study showed.

“Stethoscopes used in an ICU carry bacterial DNA reflecting complex microbial communities that include nosocomially important taxa. Commonly used cleaning practices reduce contamination but are only partially successful at modifying or eliminating these communities,” the researchers concluded in their paper.

Prior Studies to Find and Track Dangerous Bacteria

Studies tracking bacteria where people live, work, and travel are not new. For years, medical technologists and microbiologists have roamed the halls of hospitals and other clinical settings to swab and culture different surfaces and even articles of clothing. These efforts are often associated with programs to reduce nosocomial infections (HAIs).

One such study revealed that about 47% of neckties worn by clinicians carried HAIs, according to a New York Hospital Medical Center (now New York-Presbyterian Queens) study. Dark Daily reported on this finding 10 years ago. (See, “Antibiotic Neckties Are Latest Healthcare Fashion Trend,” May 25, 2007.)

And, on a larger scale, in 2013, researchers at Weill Cornell Medical College in New York City (NYC) used next-generation gene sequencing to track pathogens in the NYC subway system. The project, called PathoMap, involved collecting 1,404 surface samples from 468 NYC subway stations to develop a system for spotting and tracking potential microbial threat due to bioterrorism or emergent disease. (See, “Microbiologists at Weill Cornell Use Next-Generation Gene Sequencing to Map the Microbiome of New York City Subways,” December 13, 2013.)

This new study by UPenn Perelman School of Medicine researchers—published in a peer-reviewed medical journal—will hopefully serve as a contemporary reminder to doctors and other caregivers of how bacteria can be transmitted and the critical importance of cleanliness, not only of hands, but also stethoscopes (and neckties).  

Hospital-based medical laboratory leaders and microbiology professionals also can help by joining with their infection control colleagues to advocate for CDC-recommended disinfection and sterilization guidelines throughout their healthcare networks.

—Donna Marie Pocius

Related Information:

Molecular Analysis of Bacterial Contamination on Stethoscopes in an Intensive Care Unit

Stethoscopes Loaded with Bacteria, Including Staphylococcus

ICU Stethoscopes Teeming with Bacteria

Bacteria Remains After Cleaning Stethoscopes: Four Study Insights

Predictors of Heavy Stethoscope Contamination Following a Personal Examination

Centers for Disease Control and Prevention: Guidelines for Disinfection of Healthcare Equipment

Antibiotic Neckties are Latest Healthcare Fashion TrendMicrobiologists at Weill Cornell Use Next-Generation Gene Sequencing to Map the Microbiome of New York City Subways