Hi, I have a closed flock. All were bought together and I have never added any. I have a hen who will not stop sitting but her eggs are not fertile. I am considering purchasing a few one week old chicks from someone local to put under her to get her to stop sitting! However, I have no idea how healthy their flock is. If for any reason these chicks were hatched using an incubator from eggs of a diseased or ill chicken, would the chicks carry it and get my flock sick? Thanks for any thoughts!