If you don't make the squad you'll go into SMD, and do random things for a couple months, learning orders, driving licence things etc. Being ill shouldn't be a problem provided you can pass a PFT within a few weeks
About 6 days into my basic at Ashford chicken pox went through the squad. Hit about a dozen people if I recall-they got shoved in the trasnsit room on the bottom floor of Block 6 (which probably guaranteed them extra nasty infections) until they recovered.
Its only infectious if you touch me or steal my towels to be honest, unless your going to sneak up on me in the middle of the night and rub yourself over me, then I dont think its going to be a problem. Plus there was more than one person I spoke to on the phone who seemed to think it was ok to come down if i felt up to it.
I feel I may need a persona change on here, though there was a nice RAF dorris on site that helped me out.