We had a fight with Coryza a few years ago.
It was my understanding that even if a bird survived the infection, they were still a carrier and could infect others.
Since we were starting a breeding program, I could not in good faith ever let a bird out of here that might have been exposed to it. It spread to my young birds in a couple of weeks, and I had to put everything down. I let the yard sit vacant all winter. What I read said at least 60 days for it to die off.
Sorry to hear such a terrible thing may be happening again. 2 years later and I am still very angry with the person that would bring sick birds to an auction, and angry with myself for not following quarentine procedures.
JimD