That's interesting, LaFemme - I had two major sinus infections the first two months sober. I wondered the same thing myself. I know when people quit smoking they often get flu-like symptoms the first week, but that's probably because the membranes of the nose/mouth are in transition and more sensitive to viruses.
I often wondered if alcohol just killed the germs, and when it wasn't there anymore, it was easier to catch something. Hmmm..... another topic to research on Google!