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Study finds stethoscopes are dirtier than you think they are


March 1, 2019

Stethoscopes are maybe the most common of all diagnostic tools used in a medical facility, among the first pieces of equipment to be taken out when a patient complains of an ache or an illness. According to a new study, stethoscopes are also very dirty, much more than should be acceptable in an industry trying to reduce the number of infections spread to patients, and common cleaning methods used in medical practices aren’t working.

According to the study, published December 12, 2018 in Infection Control & Hospital Epidemiology, the journal of the Society for Healthcare Epidemiology of America (SHEA), stethoscopes carried by healthcare practitioners are loaded with diverse bacteria, including some that can cause healthcare-associated infections. The research also reviewed the effectiveness of cleaning methods, finding a standardized approach to be superior for removing bacteria compared with various approaches employed by healthcare practitioners.

“This study underscores the importance of adhering to rigorous infection control procedures, including fully adhering to [Centers for Disease Control and Prevention (CDC)]-recommended decontamination procedures between patients, or using single-patient-use stethoscopes kept in each patient’s room,” said Ronald Collman, MD, a professor of medicine, pulmonary, allergy, and critical care at the University of Pennsylvania Perelman School of Medicine and senior author of the study, in a written statement.

According to some statistics from the CDC, about one in every 20 patients has an infection after receiving medical care, and about 30%–40% of those infections happen through the spread of pathogens from one patient to another or from hospital equipment to a patient, often via the hands of healthcare workers.

Study researchers used molecular sequencing to develop a complete picture of bacteria on stethoscopes used in an ICU, including 20 traditional reusable stethoscopes carried by physicians, nurses, and respiratory therapists, 20 single-patient-use disposable stethoscopes used in patient rooms, and 10 unused single-use disposable stethoscopes as a control.

The analysis showed all 40 of the stethoscopes used in the ICU were significantly contaminated with a rich and diverse community of bacteria, including those related to common healthcare-associated infections, though the analysis could not determine if the stethoscopes ever made patients ill. Staphylococcus, the bacteria responsible for staph infections, was found in abundance on all stethoscopes, with more than half of the instruments having confirmed Staphylococcus aureus contamination. Other bacteria that can cause healthcare-associated infections, such as Pseudomonas and Acinetobacter, were also widely present on stethoscopes, though in small quantities, authors reported.

The new study is hardly the first to address the issue of dirty stethoscopes. A study published in the July 2017 issue of the American Journal of Infection Control found that medical providers rarely clean stethoscopes between patient visits, causing unnecessary infections.

“Stethoscopes are used repeatedly throughout the day and become contaminated after each patient exposure, so they must be treated as potential vectors of transmission,” said Linda Greene, president of the Association for Professionals in Infection Control and Epidemiology, in a published statement. “Failing to disinfect stethoscopes could constitute a serious patient safety issue similar to ignoring hand hygiene.”
The CDC mandates that reusable medical equipment such as stethoscopes be disinfected between patients, but the specifics of proper protocol—and whether that protocol is followed in every medical practice—is difficult to determine or monitor.

Researchers in that study observed stethoscope hygiene during a four-week rotation for medical students, resident physicians, and attending physicians at a tertiary care academic teaching hospital. Results showed that during 128 initial and 41 post-intervention observations, nobody cleaned stethoscopes.

“We anticipated low stethoscope hygiene rates but were surprised that no one performed stethoscope hygiene despite the fact that it is on the checklist for second-year medical students’ final evaluation demonstrating competency in performing a complete history and physical at our institution,” the study’s authors wrote.

Stethoscope contamination can lead to various infections, including Clostridium difficile, which causes colon inflammation and severe diarrhea.

“While the project had several limitations, it does highlight how rarely stethoscope hygiene is performed,” the authors wrote. “Standard education may not be the answer to this problem. Behavioral and cultural modification to improve hand hygiene still remains a challenge, despite being studied in large randomized trials.”

Also, a 2014 Mayo Clinic study found dirty stethoscopes at the doctor’s office as well. In that study, Didier Pittet, the director of infection control at University of Geneva Hospital in Switzerland and the study’s lead author, likened the stethoscope to an extension of the doctor’s hands, which are the main source of patient-to-patient bacterial transmission.

Healthcare personnel are bombarded daily with guidelines recommending that all workers wash their hands before and after visiting each patient, but surprisingly, no guidelines mandate that small medical equipment such as stethoscopes should be disinfected after every use.

“We have no guidelines to clean our stethoscopes, which has as many bacteria on the diaphragm of the stethoscope as we have on our fingertips,” Pittet said in a published report.

In the Mayo Clinic study, researchers had three physicians examine a total of 83 hospital patients. After each examination, they looked at the number of bacteria collected on different regions of the physician’s dominant hand and on the stethoscope’s diaphragm—the part that comes in direct contact with the patient—and tube.

Although results from 12 patient examinations showed no presence of bacteria, the remaining 71 revealed that the density of bacteria was much higher on the stethoscope than on the back and palm of the hand. The most heavily contaminated parts were the fingertips, and the more contaminated they were, the more bacteria were found on the stethoscope.

“Common sense should dictate that reusable equipment should be wiped down after each use,” said Pittet.
Bearman recommends that doctors use an alcohol-based rub to clean their equipment or use disposable covers. However, Bearman notes, many people still don't do either.

“Those hands are coming into contact with multiple potential sources of pathogens, whether it’s touching the telephone, touching the bed rails, touching the patients, touching the IV line, touching the stethoscope,” Bearman said. “So, the final common link is going to be the hands of the healthcare workers.”

How does your cleaning method hold up?

To assess the impact of cleaning on contamination, SHEA study researchers sampled 10 additional practitioner stethoscopes before and after cleaning for 60 seconds using a hydrogen peroxide wipe, and 20 more practitioner stethoscopes before and after cleaning by the practitioner according to the practitioner’s usual method, which included alcohol swabs, hydrogen peroxide wipes, or bleach wipes used for different durations.

All of the cleaning methods reportedly reduced the number of bacteria, but none of them consistently lowered contamination to the level of clean, new stethoscopes. Think of using cleaning wipes on your counter: It moves the germs around, but it doesn’t necessarily remove them from the area completely.
The standardized cleaning method reduced bacteria on half of the stethoscopes to the clean level, while only 10%, or two of the 20 tested, reached that level when cleaned by the practitioner-preferred method, leaving stethoscopes as a potential vehicle for transmission of infection.

While molecular sequencing allowed researchers to identify all the types of bacteria and the quantity of bacteria, not just specific pathogens they set out to study, the DNA test could not distinguish live from dead bacteria, so it is not clear if the stethoscopes are responsible for the spread of disease-causing agents, Collman said. Additional research is required to determine if stethoscopes are responsible for transmitting infections.

Future research should also use similar molecular approaches to identify improved cleaning methods; study bacteria present on other “non-critical” medical devices used on multiple patients, as well as in the healthcare environment; and focus on antibiotic-resistant bacteria, Collman added.

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