I would treat them all since cocci is infectious, and Corid will not harm them. That way if one gets sick 2 days from now, you don't have to start over.Thank you very much for the info. Should I separate her? Would she be OK in the barn, it's not heated? Is there a chance of my other chickens getting it? I have 13 ameraucanas/easter eggers and 6 ISO browns & 1 rooster mutt.