Right now, I don't. If I lose another bird to it (I haven't lost any in a while now), I will send it in to the Georgia Poultry Lab for a necropsy. I DO know it is either Coryza or Mycoplasmosis, because it now infects every bird I put out there. So it is something that they have, and they are carrying, even though they are better now. I even know I got it from a very horrible breeder that I went to last June to buy porcelain d'uccles from. It spread through my flock, although taking it's time to hit some of them, and the younger chicks died from it. Mostly they died from getting so lethargic, they didn't want to move, and they never ate or drank. Thus the "depression" symptoms lead me to believe Coryza.
Also, the eggs and chicks don't seem to be affected. If I read correctly, Coryza can not be passed to the egg, but Mycoplasmosis can. As long as I keep the chicks completely separate from the rest of my flock, they stay healthy and act fine. But once I decide to put a chick or chicken into the main pen with the rest of the flock (who NOW seems okay), it becomes sick.
So I DO know it's one of those two diseases that they can carry virtually forever. And I admit I don't know which one, but assumed the answer based on the healthy chicks and eggs that I'm still getting. I don't have a vet near me that specializes in chickens, and driving an hour and a half away for a diagnosis is a bit extreme. But the Georgia Poultry Lab does free necropsies, and I can bag it up and mail it to them MUCH cheaper than driving up there.
In the meantime, the ones who do get sick are brought inside, and placed on antibiotics. Usually it clears up in roughly a week.