Peter Brown on Coryza
"Coryza is caused by a very aggressive bacteria.
I would suggest Chloramphenicol eye ointment and Gallimycin and Aureomycin/Sulmet powder mixed in the drinking water for 14 days.
This disease is highly contagious and will spread to other birds if not controlled."
My flock has, through chance, never had Coryza.
All I have read says:
I highly recommend a professional's evaluation of whatever ails your flock.
Good resouces for poultry medicine are unfortunately scarce.
Peter Brown and Dr. William Patterson are two I trust.
You must, as the responsible person, be through and aggressive.
Don't call or email without a written list of symptoms and observations.
If the suggestions don't work, call/email again.
It is extremely contagious.
There is a characteristic smell that one can never forget.