But, to get weird symptoms, wouldn't it need to be something caused by someone in particular? Which then gets me back to the 'how do we get it to happen?' question. Regular colds are easier to implement as was already mentioned... it could be incoming with some of the new arrivals and just be that one little virus Acumen missed through that strange hole in the dimensional stabilizer code. However, sneezing glitter makes me think we might need something driven by someone's powers... like a spell, or a strange potion, or something like that.
Granted, I could be wrong on all of this. Hell, it's happened before.