The issue is that most respiratory infections can never be cured, permanently. That's part of what being a carrier means. Some of these diseases,which are herpes type, will stay in their body even if they seem to recover. Viruses can't be cured with antibiotics. This is the reason that if one of my birds ever contracts a respiratory illness (I'm going on four years as a chicken owner and have never had that in my flock), I will cull (yes, kill) the bird or birds that show symptoms. Period. No treatment. I want a strong flock, not one that infects any other birds that I raise and add to it and not one that must be treated every few months when they have a relapse.