The disease does not cause a significant mortality in birds over five weeks of age. Feed consumption decreases sharply and growth is retarded. When infectious bronchitis occurs in a laying flock, production usually drops to near zero with a few days. Four weeks or more may be required before the flock returns to production. Some flocks never regain an economical rate of lay.
Infectious bronchitis is difficult to differentiate from many of the other respiratory diseases.
For this reason, a definite diagnosis usually requires a laboratory analysis. Infectious bronchitis is highly contagious and does not always respect sanitary barriers. Vaccinate chickens being retained as layers. Whether broilers should be vaccinated depends upon many factors and is an individual decision. Numerous vaccines are available commercially.