My two cents from Maryland (close enough to the PA line that I can get there by bicycle!)
You're pretty close on that one! I've had to do a lot of reading up on Coccidiosis, since any new bird in my smaller run picks it up at some point. Even though it's not a virus (it's parasitic,) coccidiosis acts kinda like chicken pox, only instead of hiding in the body to wait for a weakening of the immune system, it lives in your soil. ALL soil has it, so there's no eliminating it. In fact, the little buggers in your soil are usually different from those in your neighbor's yard. Your chickens can pick up a new strain simply by visiting next door!
If you do end up with (or even suspect) coccidiosis, it's a relatively easy fix, as long as you catch it early (as soon as they start to look lethargic and heir stool goes runny.) Just keep Corid (amprolium) on hand as part of your first aid kit. It's a quick, five day treatment, and usually shows impressive results in the first 24-48 hours.
I could almost swear that the stuff is magical, but it works simply. It suppresses the B vitamins that coccidia need to survive. Unfortunately, the chickens need them, too, so as soon as the course is done, you need to put them on a good poultry multi-vitamin for a week. Without that quick replacement, I've had birds crash ... but the vitamin brought them right back. They're hardy little buggers!