Medical practice

Stethoscopes could spread hospital infections

"Stethoscopes 'more contaminated' than doctors' hands," BBC News reports after new Swiss research has suggested that the much-used instrument may spread bacteria inside hospitals, including MRSA.

The BBC reports on an observational study involving 71 patients carried out at a Swiss university teaching hospital. Doctors were asked to perform a routine physical examination of these patients. None of the patients had an active skin infection, but around half were known to be colonised with MRSA before the examination took place.

After the examination, four areas of the doctors' dominant hand (or glove) and their stethoscopes were pressed onto culture media (liquid or gel designed to support the growth of bacteria) to see how many bacteria were grown in the laboratory. Hands (or gloves) and stethoscopes were sterilised prior to the examinations, so the researchers would only find bacteria transferred onto them after the single examination.

Overall, the study found that after the examinations, the most contaminated areas were the fingertips, followed by the diaphragm (the round "listening part") of the stethoscope. The diaphragm was more contaminated than other regions of the hand, such as the skin around the base of the thumb and little finger or the back of the hand.

The study serves as an important reminder for doctors and other health professionals about the dangers of cross-contamination. Transferring equipment from one patient to another without disinfecting the items in-between could pose as much of a risk as unwashed hands. This study has only investigated stethoscopes, but the results could just as easily apply to other hospital equipment, such as blood pressure cuffs and thermometers. 

Where did the story come from?

The study was carried out by researchers from the University of Geneva Hospitals and was funded by the University of Geneva Hospitals and the Swiss National Science Foundation. There were no reported conflicts of interest.

The study was published in the peer-reviewed medical journal, Mayo Clinic Proceedings.

The reporting of the study is generally accurate, but all of the sources that reported on it (BBC News, ITV News and the Mail Online website) made the mistake of claiming that stethoscopes were more contaminated than doctors' hands. This is not strictly true.

What the study actually found was that fingertips were most contaminated, followed by the "listening part" of the stethoscope that comes into contact with patients' skin.

What kind of research was this?

This was an observational study carried out at a Swiss university teaching hospital. After normal physical examination of patients, doctors' hands (or the gloves they used during the examination) and stethoscopes were pressed onto culture media (a substance that can support the growth of bacteria) to see what bacteria were grown in the laboratory over a period of five months.

As the researchers say, the transmission of bacteria and other micro-organisms between patients poses a significant risk to the health of patients staying in hospitals and increases the risk of death.

There is a wealth of evidence that healthcare workers' hands are one of the main routes of cross-contamination. However, there is a lack of evidence supporting the role that medical equipment such as stethoscopes play as sources of contamination.

The researchers say that they aimed to compare doctors' hands and stethoscopes immediately after examination to see if stethoscopes could pose as much of a risk for cross-contamination as unwashed hands.

What did the research involve?

The study was conducted between January and March 2009 at the University of Geneva Hospitals. The researchers included a sample of adult patients from medical or orthopaedic wards who were in a stable medical condition and did not have an obvious skin infection. However, they also included a sample of people who were found to be colonised with methicillin resistant Staphylococcus aureus (MRSA) on standard hospital admission screening.

Three doctors were involved in the tests and the study involved two phases. In the first, they wore sterile gloves to ensure the initial bacterial count on their hands would be zero. This study specifically involved the people free from MRSA and aimed to look at the total count of (aerobic) bacteria after examination.

In the second phase, the doctor examined the patients without gloves, but prior to the examination they used alcohol hand rub following the technique laid out by the World Health Organization (WHO), which recommends rubbing the hand rub in for 30 seconds.

This part of the study specifically involved the people with MRSA colonisation and aimed to look at transmission of MRSA.

The stethoscopes used by the doctors were sterilised prior to each patient examination.

After the examinations, four regions of the physicians' dominant gloved or ungloved hand were sampled for bacteria. Two sections of the stethoscope were also tested, including the diaphragm and the tube attached to it.

Sampling was done by pressing the regions being studied onto culture plates. After culture for up to 24 hours, the researchers examined the total count of (aerobic) bacterial and MRSA colonies.

What were the basic results?

The first study included 33 patients without MRSA (64% male, average age 62). The second study included 38 patients with MRSA colonisation (58% male, average age 72). Around a third of the patients in each study were receiving antibiotics.

In the first study, of the regions tested, the fingertips were most heavily contaminated with bacteria, with a median of 467 colony forming units per 25cm2.

Colony forming units, or CFUs, is an estimate of viable bacteria numbers; in this case, the amount of bacteria contained in an area of 25cm squared, which is roughly equivalent to the size of a small hardback book.

Fingertip testing was then followed by testing of the diaphragm of the stethoscope (median 89 CFUs/25cm2).

Further testing involved:

  • regions around the base of the thumb and little finger (around 35 CFUs/25cm2)
  • the stethoscope tube (18 CFUs/25cm2)
  • the back of the hand least used (8 CFUs/25cm2)

On statistical comparison, the contamination level of the stethoscope diaphragm was significantly lower than the contamination level of the fingertips, but significantly higher than around the base of the thumb or little finger or the back of the hand.

In the second study, where 38 patients with MRSA were examined, the pattern of contamination was similar, though with lower colony levels. The most heavily contaminated region was the fingertips (12 CFUs/25cm2), followed by the stethoscope diaphragm (7 CFUs/25cm2), then around the thumb or little finger.

However, the stethoscope tube and back of the hand had no MRSA. There was also no significant difference between contamination of the stethoscope diaphragm and fingertips.

In both studies, the level of contamination on the stethoscope was related to the level of contamination on the fingertips.

How did the researchers interpret the results?

The researchers concluded that, "These results suggest that the contamination level of the stethoscope is substantial after a single physical examination and comparable to the contamination of parts of the physician's dominant hand."


This study demonstrates that after a patient examination with sterile hands and stethoscope, the part of a doctor's hands most highly contaminated with bacteria was the fingertips, followed by the diaphragm of the stethoscope.

This part of the stethoscope was more contaminated than other regions of the hand, including the skin around the base of the thumb and little finger, or the back of the hand. The pattern was similar when looking at MRSA and total bacterial count in general.

It must be acknowledged that this study was small, involving the examination of only 71 patients by just three doctors at a single Swiss hospital over a period of five months.

However, the scenario examined – where hands and stethoscope were sterilised prior to use, and the patients involved were in a stable medical condition and did not have an active skin infection – should mean they are fairly representative of the "best situation" that could be found if similar tests were carried out in hospitals elsewhere.

In other "less than best" situations, such as where doctors' hands and equipment haven't been completely sterilised prior to use, levels of contamination could be much higher than those seen here. As the researchers say, no piece of equipment used on patient wards can be fully sterile, and most objects in the healthcare environment will yield some micro-organisms when sampled.

However, what is difficult to say is the clinical significance of detecting these levels of contamination. This study didn't test whether transferring the level of bacteria contamination detected on fingertips and stethoscopes would result in infection if it was then transferred to another patient without sterilisation.

But it is plausible that if repeated examinations were conducted without sterilisation in-between, the contamination would get worse and may be more likely to pose an infection risk, particularly to vulnerable patients.  

A useful follow-on to this study would be to investigate how effective different methods for decontaminating stethoscopes are at reducing bacterial counts. That is, while clear WHO guidance is in place informing the process by which hands need to be sanitised to make them "safe", similar guidance for other equipment, such as stethoscopes, is not available and would be useful.

Overall, this study serves as an important reminder for doctors and other health professionals about the potential risks of cross-contamination if hospital equipment and hands are not disinfected between one patient and the next.

NHS Attribution