I know this may sound harsh to many, but I would cull all of the chicks, and any unwanted roosters too. To keep them, treat them and possibly sell or give them away could spread it to someone else unsuspectingly. Culling and cleaning effectively afterwards, then starting over. I know it sounds harsh, but sometimes its the best option when you are struggling to get ahead of it like this.
First state quoted below, you can find Amprolium (Amprol) for sale here:
http://www.firststatevetsupply.com/store/index.php?cPath=21_29
Very interesting article, Celtic. I learned a lot. I did not know that there needed to be repeated exposure. I agree with you that it would be best to cull the chicks. I think a seller could quickly loose their reputation selling birds that do not have a strong immune system. I want only the strongest of my chicks in the flock, but I sure don't want to introduce problems from outside. Dumb question I know, but can cocci be transmitted through eggs?
Cindy