@dls You're not overthinking - just doing your due diligence. The answer, at least in my clinic, is that you either bring the packaged sample with you and deliver it directly to the lab, or the sample is taken in an exam or procedure room that goes through a thorough decontamination cleaning afterward.

The other thing is that MAC/NTM are not spread person-to-person via nasal droplets like the flu. They are spread by prolonged time in your lungs, where they have arrived airborne contaminated soil, dust or contaminated water mist inhaled in quantity. I suppose it could happen that an infected person might sneeze droplets directly into your nose or mouth on the elevator, but...

Does this make you feel more comfortable?
Sue