Glad to know my doctors don't cause any harm by looking professional.An oft stated belief, not backed up by facts. Additionally, I son't know about you, but I wear a jacket with my tie. This or a lab coat prevents it from contacting the patient. Better to clean one's stethoscope between exams (sometning I very rarely observe others doing), or else change ones jacket and shirtsleeves between exams.
Here is an excerpt from the CDC's position.
The Centers for Disease Control and Prevention (CDC)’s Guidelines for Environmental Infection Control in Health-Care Facilities state that, “although microbiologically contaminated surfaces can serve as reservoirs of potential pathogens, these surfaces generally are not directly associated with transmission of infections either to staff or patients. The transferal of microorganisms from environmental surfaces to patients is largely via hand contact with the surface.”