
Besides strains of cocci varying from one area to another, cocci in general are more prevalent in some areas than others -- more common in wet areas, unusual in deserts. Where I live, a low lying area, it is nearly impossible to buy unmedicated starter or grower. I don't know how much of that is locals feeling "better safe than sorry" and how much is actual problems. I've raised several groups of chicks and have not had a case of cocci that I know of.
Ridgerunner gave you some good advice, IMO.