Hey Doc! Wash your hands—and stethoscope.

When a doctor comes at me with the stethoscope, I usually start shivering, just thinking about how cold it will be when it hits my chest. But a first-of-a-kind study by Swiss researchers got me thinking that maybe I should be shivering with fear, too. Why? Because it turns out the devices are often covered in dangerous bacteria.

It's well established that bacteria can be spread by unwashed hands. And a few studies over the years have found that clothing (such as ties) and medical instruments (such as stethoscopes) can also transmit bacteria. New guidelines, in fact, aim to reduce the risk of infection from doctor's clothing. But this new Swiss study, in the March 2014 Mayo Clinic Proceedings, quantifies just how contaminated stethoscopes can be.

In the study, 71 patients were examined by one of three randomly selected doctors. Researchers then analyzed the hands and two parts of the stethoscope (the tube and the diaphragm, or the part that is always so cold) for bacteria, including the notorious MRSA.  Surprisingly, the stethoscope's diaphragm was more contaminated with bacteria than all the areas of the hands, except for the fingertips. And the stethoscope's tube was more contaminated with bacteria than the back of the hand. 

That's worrisome, for two reasons. First, doctors carry their stethoscopes throughout the hospital and use them over and over on hundreds of patients. Second, surveys show that 70 percent to 90 percent of physicians don't routinely disinfect their stethoscopes after examining the patients. And, our work on hospital acquired infections documents just how common and dangerous the infections can be.

To prevent those infections, we've long suggested that before you let any doctor or nurse touch you in the hospital, you ask whether they've washed their hands. This new study suggests that you should also ask the medical staff whether they've washed their stethoscopes.

Read more about how to avoid hospital infections.

—Chris Hendel