Mystery Work Illness

For the past week or so, my sister has been waking up every morning with her lips swollen and hives all over her body. These subside in a few hours and she feels no worse for wear. When she asked me about it, I said “this sounds environmental—ask your neighbors if the same thing is happening to them”. No results. So then I said “ask your coworkers”. Paydirt. Five of her coworkers are exhibiting the exact same symptoms. One of them went to her doctor, who basically threw up his hands and said “I dunno”. He gave her cortisone, which did nothing. So, what can the offending agent be? I’m guessing a cleaning compound. Any other ideas? They all work on the floor of a Las Vegas casino. Something in the air conditioning system, perhaps? I’ll probably find out pretty soon after the OSHA gang does their stuff, but I just want to see what you guys think.

I’ll weigh in with two possibilities: mold in the A/C (although this would probably build up gradually) or a pesticide. Had they sprayed for anything lately? Any other characteristics that unite the 5 affected employees?

The Casino is owned by Grey Aliens who are performing some kind of experiment?