C.
I would give it 4 months and see how it goes. When my daughter was 12 months we started her at day care and for the first 2-3 months, we were home with her once a week for something. After that, she made it through the next few years with very few problems. My son started at 8 weeks and I had expected it to go bad but he was a lot better and only had a few sick days. On the positive side, if he is getting a lot of colds and things now, he will probably have a much easier time when he starts school because he will have already been exposed to everything.
If you think the overall condition of the center is dirty, there is a good chance they are not cleaning as often as they should which could be part of the problem. I know at my last center, when pink eye or strep throat would go around, everything was disinfected and they even washed all the stuffed animals.