Hey Carol,
What feed are you offering? Is there grit and oystershell available free choice? Are you still having problems getting the one to go in at night? How is the roosting situation, and could they be laying outside the nest box?
Jess,
if you suspect desease you need to quarentine and seriously concider culling. Now with that said what makes you thin there is something wrong? If the chick does have it you need to keep all new hatches far away, and be sure you practice bio security to prevent spreading. Where have you looke fo the vaccine so far?