Just wanted to give you a little more information on cocci and coccidiosis.......
Cocci are not a virus, so not contagious in that fashion. They are more of a protozoan type organism, but they can spread through a flock quickly under the right circumstances. They spread like most parasites, when they are ingested. They are shed in the droppings of infected birds. So with chickens scratching and pecking, the spread can be rapid. Adult birds who have been exposed do build immunity. Having said that, there are about 8 different strains of cocci, some more virulent than others, and they build immunity to those they have been exposed to. So if you have cocci, and bring in new birds, they may be susceptible to the cocci you have. If you bring in new birds that are carrying a new strain, then your current birds are susceptible. And adult birds that are immune compromised in any way can become sick even from a strain previously exposed to. Chicks are extremely susceptible to cocci, and the cocci tend to thrive in warm, wet or damp conditions, which makes brooders a prime area.
Cocci can survive in the soil indefinitely, there is really no way to eradicate them. Keeping your area as clean as you reasonably can, as dry as possible, and free of build up of droppings are the best prevention. Try to remedy areas that tend to stay wet or damp.
Medicated chick feed can help prevent outbreaks in chicks, but it will not treat an actual outbreak. So with an outbreak you will need to treat.
If you are using Corid (amprolium) then the treatment is pretty safe. For your older birds it's going to be a judgment call on your part. You can either go ahead and treat, or just wait and observe for signs of illness and then treat. I generally treat the entire flock when I have an outbreak. But either way, you need to make sure that the treated water is the only water the treated birds are getting.
Having cocci is not a reason to panic, just a reason to learn as much as you can, be aware of the symptoms, and be observant of your birds to catch the onset as early as you can. And I always follow treatment with vitamins for a few days, after treatment is complete.
On the encouragement front, I have cocci in my soil and have dealt with several outbreaks, but am in my third consecutive year without an outbreak now (knock on wood!), and have raised several batches of chicks, both brooder raised and broody hen raised during that time.
Best of luck!
