During 32 years as a physician, Daniel Federman has used his stethoscope to listen to patients’ hearts and lungs. But a recent study at the West Haven, Conn., veterans’ hospital where Dr. Federman works left him aghast. After seeing an image of the bacteria accumulated on his stethoscope, he admits, “I was appalled…The basic fact is that I don’t recall cleaning my stethoscope”—ever.