The admonition to physicians and other healthcare workers to wash their hands before and after patient contact is well established (thanks to Ignaz Semmelweis) and has become part of professional conduct. By engaging in this process the transmission of pathogens--carried on the hands of a provider--between patients is diminished.
However, even if hands are washed there may be other mechanisms pathogens can exploit to find new individuals to infect. A study, just published in the Mayo Clinic Proceedings, assessed the ability of a physician's stethoscope to be a vehicle of bacterial transmission.
The study showed that the rate of stethoscope contamination was comparable to that of unwashed hands.
The implications of this study are many. Stethoscopes are the tools of the trade of medicine and many physicians exhibit their own "flair" with their stethoscope (color, style, electronic features, engraving, etc). Just like it's been difficult to diminish the prevalence of physician white coats, despite evidence that they may also be routes of contagion, personal stethoscopes may be hard to dislodge. Disposable patient-specific stethoscopes may be somewhat helpful but I believe total disruption of stethoscopes, by hand-held ultrasound devices, is likely to provide the best solution.