Sadly, they are all exposed to what is going through the flock.
Respitory illnesses tend to be chronic and birds that survive become carriers that can affect others. There are alot of threads on this topic that you can research and lots of experienced folks that can provide great feedback.
If you are attached:
The antibiotic will help them get over the infection brought on and clear them up for now.
Vet RX for poultry rubbed into their nostrils, combs, and wattles helps them breath easier and can help protect the birds that do not have it yet. Make sure to wash hands after contact with sick birds so you do not accidently rub the germs on the healthy ones.
Also, use Oxine to spray around coop to disinfect and kill airborne germs.
The flock would need to be treated as a closed flock as there is strong possibility of survivors being carriers of the virus through the rest of their lives. The illness will pop up when the birds are stressed.
If they are more of livestock then pet and you raise for selling then you will need to cull them and start new. (disinfect coop real well and let sit for minimum of 30 days before adding new birds. most virus cannot live longer than this outside of the birds)
