I disagree coq au vin...I have had a problem lately with chicks having CRD, but before that I posted a thread wondering why my rooster was sneezing and after a few days of that being his only symptom he got better with no intervention whatsoever. Later my andalusian did the same thing and healed with no intervention. If sneezing is the only symptom, no runny noses, coughing, bubbly eyes, etc, I would just add some vitamins to the water and cull only those who exhibit some additional symptoms listed above. Why kill chickens who may honestly not have CRD? And from what I have read on this forum ABOUT crd, once you have it in the area, you are basically doomed to keep it so long as you have chickens and there is no cure so why kill all chickens, including those asymptomatic, and not be able to have any at all? I personally prefer to treat the curable sicknesses with electrolytes/vitamins, and only destroy the truly "sick" chickens who will not improve with treatment. That has worked for me.
OP, if you try searching "sneezing chickens" you will find many threads wherein there are various reasons not related to CRD for chickens to sneeze.