Had eye infections, ear infections and throat infections go through my daycare a few weeks ago. having another round of ear infections again in a few kids.
For myself I don't close to clean. I don't get paid if I close so unless I am really sick I don't close. I always tell all parents if something is going around. If one kid is home sick I share with everyone. This way if their child is showing similar symptoms they realize it could be the same illness instead of just brushing it off and blaming it on teething, something they ate etc.
When an illness goes through daycare I usually spray the play room/toys down with Lysol every evening. The kids don't share beds or bedding so I will wash the sick child's bedding while they are home (they shouldn't be at daycare with eye infection until on antibiotics for 24 hours providing it isn't extremely contagious - if it is they should be home until it clears up). I just make sure everyone is washing hands more and keep reminding little ones to keep their hands out of their mouths (and toys too).