While red poop is a big red flag that you need to check them out, not all red poop means blood. It could be shed intestinal lining, it could be something they ate. Feed you chickens cooked beet skins and expect to see red poop the next day. Red cabbage can turn their poop blue.
After being exposed to one strain of cocci for two to three weeks the chickens develop an immunity to that strain. That does not mean they are now immune to all strains, just the strain they were exposed to. As long as the numbers in their guts do not get out of control, you’ll never know they have it. After three weeks of continuous exposure you don’t have to worry about it. They are immune to that strain. That does not mean you can them let everything stay wet and muddy. That’s still unhealthy.
I feed my brooder raised chicks some dirt from the adult run on day 2 or 3 in the brooder to get them started on developing immunity. Since I keep my brooder very dry that interrupts the life cycle of the bug that causes cocci so I give them more dirt every three or four days so they have continuous exposure. I’ve never seen a brooder raised chick with any signs of cocci.
I had a couple of broody raised chicks get cocci once. The weather set in really wet and the run stayed wet and muddy. The cocci bug thrives in wet poopy mud and evidently they ate enough that the numbers got out of hand. They were locked in the run because I had a fox problem that took a while to take care of. I haven’t had any cocci problems since I got the electric netting. The broody hens can now take them out of the mud and onto grass.
Bridebeliever, just because your chickens did not come down with cocci that time does not prove you do not have cocci in your flock. They can easily have immunity to any strain in your ground. The risks are usually new chicks too young to have immunity, new birds coming in, or a new strain of cocci gets introduced.