I'm glad you had it cultured to diagnose so you could make a decision based on what's really going on rather than just guessing.I want more and I sell the eggs and ( no eggs are not affected unless you hatch them ) I cant do that with this illness, if people were to find out it would kill my sm business. and I cant watch them suffer, this is a painful thing to the birds.
I have chosen to cull my whole flock. Not a thing I want to do but some of these hens I have a bond with and I refuse to see them go through this.
I was just reading an overview of Coryza last night. It did say that it is not egg transmitted so if there are some of your current birds that you would want chicks from you could hatch some of them - as long as they aren't exposed to the adult carriers after hatch.
I can't imagine how hard it is to cull the whole flock and I hope I never find out. But I do applaud you for having the courage to make that decision as a part of responsible husbandry. Your willingness to take good care of your birds is an example to us all.