Researchers say stethoscopes should be disinfected after each patient contact, after a study found the instruments are more contaminated than doctors' hands after a single physical exam.

The study, published Thursday in the Mayo Clinic Proceedings, compared the level of bacterial contamination found on doctors’ hands and stethoscopes after they examined a patient.

During the study, a total of 83 patients at the University of Geneva Hospitals in Switzerland were examined in 2009 by a physician.

After the examination, the tube and diaphragm of the stethoscope and four different parts of the doctor's dominant hand (the back, fingertips, base near the thumb and base near the little finger) were assessed for the total number of bacteria, including bacteria that have become resistant to antibiotics (methicillin-resistant Staphylococcus aureus).

The study found that the diaphragm of the stethoscope was more contaminated than every single part of the doctor's hand except for the fingertips. Also, the tube of the stethoscope was more contaminated than the back of the physician's hand.

The study's lead author Dr. Didier Pittet said the results show that stethoscopes need to be disinfected after every use.

"By considering that stethoscopes are used repeatedly over the course of a day, come directly into contact with patients' skin, and may harbor several thousands of bacteria (including MRSA) collected during a previous physical examination, we consider them as potentially significant vectors of transmission," he said in a statement.

"From infection control and patient safety perspectives, the stethoscope should be regarded as an extension of the physician's hands and be disinfected after every patient contact."

The researchers found that there was an association with the contamination level of the stethoscope diaphragm and the contamination level of the fingertips. As well, the contamination level of the stethoscope tube increased as the finger tips became more contaminated.

Didier said more research is needed to determine what are the best methods of disinfecting stethoscopes.