An iconic symbol of medicine, the stethoscope can serve as a fomite to transmit pathogens from patient to patient if infection control procedures are not followed, researchers report.

“Stethoscopes used in an ICU carry bacterial DNA reflecting complex microbial communities,” they found.¹ “Commonly used cleaning practices reduce contamination but are only partially successful at modifying or eliminating these 30 communities.”

Traditional culture studies have found pathogens on stethoscopes, raising the theoretical risk of transmission from patient to patient.

“It is well documented that practitioner stethoscopes are not routinely disinfected, and studies based on bacterial culture show that they may be contaminated with potential pathogens including methicillin-resistant and -sensitive Staphylococcus spp, multidrug-resistant P. aeruginosa, Acinetobacter spp, Enterococcus spp, Escherichia coli, Klebsiella spp, and Streptococcus spp.”

Using new gene sequencing techniques, the researchers quantified the bacterial populations on 17 stethoscopes in use in an ICU.

“The important message is that it introduces a new methodological approach to do the type of infection control tracing that is typically done with culture methods,” says lead author Ronald Collman, MD, professor of medicine in the Abramson Cancer Center at the University of Pennsylvania School of Medicine in Philadelphia. “It reminds us that maximum adherence to the most stringent infection control procedures is really required. Even these things people generally don’t think about — stethoscopes as vectors. Maybe they could be.”

The study by Collman and colleagues included individual provider scopes, designated patient-room stethoscopes, and 18 clean, unused individual-use stethoscopes. “Bacterial contamination levels were highest on practitioner stethoscopes, followed by patient-room stethoscopes, whereas clean stethoscopes were indistinguishable from background controls,” they report.

Microbes linked to healthcare-associated infections (HAIs) included Staphylococcus, which “was ubiquitous and had the highest relative abundance (6.8%–14% of contaminating bacterial sequences).”

“Cleaning of practitioner stethoscopes resulted in a significant reduction in bacterial contamination levels,” but in some cases, bacteria persisted.

“At our institution, when we have a patient who has a known MRDO [multidrug-resistant organism], not only do we use gloves and gowns and personal isolation, but we put a single-use stethoscope in that room,” Collman says. “That is only used with that patient, and when the patient is discharged, we throw away the stethoscope.”

Although there is not a documented case of transmission of infection to a patient via a stethoscope, the possibility of it informs such infection control efforts, he says.

“In the last decade or so we have new methods where you can sequence the DNA,” he says. “It can tell you the relative abundance of the various types of bacteria. To our knowledge, this is the first time stethoscopes have ever been analyzed for bacteria using these molecular methods.”

Bang Worth Buck?

Hospital Infection Control & Prevention sought further comment on this issue from Hilary Babcock, MD, president of the Society for Healthcare Epidemiology of America. Babcock was not involved in the study.

HIC: The study found evidence of pathogenic genetic materials on stethoscopes, but one might expect that in a hospital.

Babcock: It is not surprising that bacteria will be found on devices used in a healthcare setting. That’s one of the reasons we put patients with MDROs and resistant organisms — for which we don’t have a lot of treatment options — on contact precautions, dedicated equipment, and single-use stethoscopes. We want to try to avoid spreading the highest-risk organisms from patient to patient on the stethoscope. And, of course, it is the same reason we recommend hand hygiene in between patient care. There are existing recommendations that stethoscopes and any equipment that is used between patients should be cleaned.

HIC: Is it possible to quantify the risk of stethoscopes to patients?

Babcock: It is certainly a potential risk, but it is hard to quantify that risk directly to patients. It is notable as well that the authors do point out that some of the bacteria that would be of more concern are present in low levels, and that they cannot determine from the kind of testing that they did whether the bacteria are viable or not — because it is molecular testing. We don’t know if [the bacterial contamination] got on the next patient whether that could cause an infection or not. I think it will be interesting for them to try to match up strains with patient infections in [a subsequent study].

HIC: We have also seen these bacterial contamination studies involving provider white coats and neckties that may contact the patient. Is it worthwhile to fight these battles on stethoscopes and ties when it is still hard to get people to wash their hands?

Babcock: It’s a fair question. These studies are interesting and they highlight potential risk, but as we know, there are bacteria all over the hospital. It is not a sterile environment. I think it makes sense to focus on areas of significant risk, and it is hard to quantify the risk associated with this finding. I agree people are still trying to get higher levels of hand hygiene, and healthcare workers’ hands touch the patient and touch invasive devices. Usually the stethoscope is placed on intact skin.

Again, this is not ideal, and we certainly don’t want to be moving bacteria that could cause infections between patients. But it is hard to quantify the risk to focus our efforts.

REFERENCE

1. Knecht VR, McGinniss J, Shankar H, et al. Molecular analysis of bacterial contamination on stethoscopes in an intensive care unit. Infect Control Hosp Epidemiol 2019;40:171–177. doi: 10.1017/ice.