Quoting the wise Homer J. Simpson: "If you don't try, you can't fail".

Well actually I'm not sure if I agree with that.. I don't really even see whats the big issue really. Maybe you can call them the day of the visit and try to hear if they are having the sniffles and suggest you re-schedule until they feel better if they don't sound well. TBH I'm a lot more worried about using say public computers or pressing elevator buttons which I know are covered in germs than talking to random people. then again I don't know anything about contiguous diseases so take what I say with a mountain of salt