Thank you for the question for I learned something new, had no idea of MAC, know I do! I had contracted Valley Fever it to lives in the soil as your bacteria does, interesting.
I agree with both gentlemen and on this one. Standing in public service like she does all day long and asking people all day, "How are you today" or similar is pretty boring for the same answers come back to her. I give the cashier credit for being alert and paying attention to those she/he is helping instead of making you feel like your dealing yet with one more machine / computer in our lives. Also if the cashier used the right terminology she/he either is experiencing something personal to do with their lungs or a close family member, maybe a child, partner or parent, and willing to share information or maybe needed information. Then again, this person could be in some sort of medical schooling and just using their knowledge at their part time job to make their way to their goal? My favorite person when I am asked questions or being stared at is small children, they are just curious in wonderment. I will actually answer even if the parent is standing there apologizing for the child's actions and let the know I am ok with the questions. For those that are staring, I start the conversation with them about what they are looking at and explain what it is then answer any questions they might have. Funny how each time the parent thanks me for sharing with the child after the fact. There has been a few times where a parent has even asked a couple questions once conversation is moving along. People / humans are curious beings!
I hope one day you will feel more comfortable using your POC in public, I am so looking forward to receiving mine soon that I am full of excitement for I will be able to do so much more and will not be limited to how many pull along tanks are needed to make a trip to the place of interest including a grocery store. I wish you well and hoping you are breathing easier.