I bought 3 chicks from a breeder of Cream Legbars. I put all 3 in quarantine for 2 weeks, then gave one to my sister. My 2 were shy and lethargic and didn't act normally around food, so I kept them in quarantine for just over a month. I tried to introduce them to my flock, but they were viciously attacked, so I put them back in quarantine. Then they got sicker (probably from that stress!) and died. And also passed it on to the rest of my flock. Even though the stinky chick died, and was only in with my chickens for a few hours, now I can smell the stink on the others.
My sister noticed her chick wasn't well and got it diagnosed by a chicken veterinarian as Coryza. So now both our flocks are infected. Ugh. Her chickens also have a virus that causes tumors, which she discovered after she started a surgery on one of her hens and ended up euthanizing it (my sister is also a vet, just not primarily a chicken vet).
I think we are going to go with closed flocks for now, but I have a new coop (in a new area of the yard) in the works, and perhaps when the time comes to get that set up, I may set it up with all new birds, and cull off my current flock. It'll be sad, though. Really sad!
From what I've read, it doesn't sound like it can be transmitted through eggs. If my current hens and rooster make some fertile eggs, can I put them in an incubator and hatch out healthy chicks? It may ease the sting of culling, especially for the kids, if they know we are raising the babies of our old chickens. Will fertile eggs from Coryza-infected adults be clean, or will the chicks be infected (even if the adults are culled before the babies hatch)?