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Stethoscopes have always been an obvious suspect in the transmission of infections to patients by health care professionals. They're carried room to room, come in contact with each patient, and are almost never disinfected between patient contacts.
Testing has shown just what one would expect: stethoscopes are often contaminated with bacteria. One of the latest new studies showed that on 40 stethoscopes used in an ICU at University of Pennsylvania's medical center, Staphylococcus aureus DNA was present on 24. (The tests they used could not differentiate methicillin-sensitive staph from the more-feared MRSA). Most of the stethoscopes also carried Pseudomonas or Acinetobacter, and about half had Stenotrophomonas, Enterococcus, or Clostridium populations.
Attempts at cleaning were usually of limited effectiveness. Authors sampled practitioner stethoscopes after a standardized cleaning method using a hydrogen peroxide wipe for 60 seconds, and after the owner's preferred method (such as alcohol wipes or bleach wipes).
The standardized cleaning method reduced bacterial DNA levels to the predetermined "clean" level in only half of stethoscopes. When practitioners cleaned their stethoscopes using their personal preferred method, only two of 10 were considered clean on re-testing.
"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," the lead author said in a statement.
Each hospital and ICU has its own unique ecology of micro-organisms (hence the need for individualized antibiograms) and each hospital might get a different result by repeating this small single-center study. However, it's likely their results would be similarly stomach-turning and concerning.
Another study from 2018 showed that stethoscopes were disinfected in accordance with CDC guidelines fewer than 1 in 25 patient encounters, and more than 80% of the time not at all.
This all is dismaying news to the practicing intensivist, who enjoys feeling fresh at work, and wants to avoid spreading dangerous bacteria to patients -- but who also likes being able to actually hear something through a stethoscope, which isn't usually possible with the $1.99 disposable models.
Those who want to actually learn how best to clean their stethoscope will have to do some research. In a remarkable feat of bureaucratic obscurantism, the CDC managed to publish an entire 161 page guideline document entitled "Guideline for Disinfection and Sterilization in Healthcare Facilities" without ever explaining how to clean a stethoscope properly; nor does its web page. Internet searches mainly reveal manufacturer guidance, advising use of isopropyl alcohol, which was considered ineffective in this study.
It's not yet been demonstrated how often bacteria are actually transmitted to patients from contaminated stethoscopes -- although advances in DNA sequencing technology may make this feasible in the near future. If confirmed as infection vectors, stethoscopes' status as treasured, occasionally useful totems of the ritual of medicine might fade into anachronism. (Or doctors could scrub them with disinfectant for two minutes after every use. Which do you think is more likely?)