No chickens here before, well maybe 100 years ago, but even that is not for sure...chicks were on the ground a couple hours, about a week after stopping medicated feed and they got it. No bloody stools but all the other symptoms...and I am VERY careful about my biosecurity also.
Like I said, the only way to TRY to not get it....there is always that chance...we got it! We have had an unusually wet summer, one really hot spell for a week or so, then cool weather and more rain...and again, they were stressed too...stress will cause an overload, which is when they get sick. Chickens can carry a certain amount of cocci and not be sick, it is only when they are young and their immune systems are not fully functioning, sick birds from other diseases, or stressed are the most common ways they get sick from cocci. We have no other birds either, just started again, in poultry, in a different place from before. So Yes, there are no guarantees, but the best way to try not to get it, is to feed medicated feed! You can feed it right up to near POL.