I brought it home from a swapThe bantam cochins I got looked healthy and were quarantined for a month. When I put them out with the rest of the flock, everyone, including the turkeys got sick. So did the young ones I had inside in the brooders. There was quite a lot of chatter on the swap's Facebook page as several buyers had the same thing happen. I did a lot of research and talked to others familiar with the disease and used Denagard (a swine medication) to wipe it out of my flock. Often you don't know your flock has it because they don't appear sick, but there is decreased egg laying and loss of appetite so your birds look a bit scrawny. You also have poor hatch rates and often the chicks die before they are two weeks old. One of the ways you can tell it is eradicated is that fertility of the eggs is way up and the chicks are vigorous and grow well.
There are estimates that 80-90% of backyard flocks are infected. Like someone else stated, wild birds carry it. So there is no cause to obsessKeep an eye (and ear) out for sniffling, sneezing and gurgling and treat right away. What I had was a very virulent strain and I saved all my birds. If you search this site for denagard and MG there is a wealth of information. The turkeys were especially bad because they have such small heads and sinuses. After the first dose of denagard they looked better by the next day and all pulled through. The only aftereffect was some swelling in the face that took about a year to go away. It isn't approved for poultry in the US, but is used in most of the rest of the world. Good stuff, and has no withdrawal period because it is not a med taken by humans. It goes in their water and is easy to administer, you just have to keep it away from waterfowl because they drink so much water they OD (I lost a duck hen that way).
So sorry for the trouble you went through.