The stethoscope may be the iconic medical tool that most doctors cannot do without, to diagnose and cure their patients' illnesses. Unfortunately, it may also be a cesspool of germs that could spread bacteria from one patient to another.

In the study "Contamination of Stethoscopes and Physicians' Hands After a Physical Examination" published in the March 3 issue of Mayo Clinic Proceedings, researchers evaluated the level of bacterial contamination between sterile stethoscopes and doctors' hands after a single physical examination of 83 patients at a university teaching hospital in Switzerland.

The researchers measured the amount of bacteria found on the doctor's fingertips, ball of the thumb, palm and back of the hand, as well as the tube and diaphragm of the stethoscope used following the doctor's physical examination of each of the patients carried out using a sterile stethoscope and sterile gloves. They particularly looked for levels of contamination of MRSA (methicillin-resistant staphylococcus aureusis), a strain of bacteria resistant to a number of widely used antibiotics.

 The researchers found that while the doctors' gloved fingertips carried the most number of bacteria, the diaphragm of the stethoscope was more contaminated than all the other areas of the doctor's hands. The stethoscope's tube was also more contaminated than the back of the doctor's hands.

"By considering that stethoscopes are used repeatedly over the course of a day, come directly into contact with patients' skin and may harbour several thousand bacteria (including MRSA) collected during a previous physical examination, we consider them as potentially significant vectors of transmission," said study author Didier Pittet, director of the Infection Control Program at University of Geneva Hospitals in Switzerland.

The researchers also observed that the contamination level of the stethoscope's diaphragm and tube correlate with the amount of bacteria found on the doctor's fingertips. "Although infection cross-transmission from one patient to another has not been demonstrated in this study, it seems clear that staff and doctor stethoscopes constitute an extension of their fingertips in terms of risk for germ's cross-transmission," Pittet said.

The researchers said their findings show the importance of disinfecting the stethoscope after each use to prevent the spread of infection.

"Germs are acquired from the patient's skin in contact with the stethoscope, the same way hands usually get colonized with the patient's germs," Pittet said. "The important implication is that the stethoscope, whether used by a doctor, a nurse, an assistant nurse or any staff, needs to be cleansed after each use."