When we breathe the air coming from sick people, our Immune System must kill all the fungus and expell the waste. Once we are sick, then it makes this a harder job.
I can breathe the air of old order Amish for 10-30 minutes and then my sweat will stink like the Amish smell for 3 days. Now consider if I had to work 8 hours a day around sick people, in no time at all, my body would be so sick I could not pass off so much disease and I would be as one with them.
People rarely stop to consider they are what they BREATHE.