If there's one thing I've learned from my recent and ongoing experience with respiratory illnesses, it's that many diseases and problems, can have the same symptoms, which is why the most experienced folks on here were telling me from the start of it all, to get a necropsy done. They were right. I soon had a pullet die in the first few days of seeing symptoms in my new pullets and my cockerel (almost 1 yr old). They had sneezing, coughing, diarreah, pullets drinking lots of water and eating, while cockerel wouldn't eat or drink, pullet standing off by itself not doing anything, fluffed up, eye pupil looking off to the side. runny nose, and cockerel had mucas in his mouth. He was in serious condition (3 days after the new pullets came). I was told it could be Coccidiosis, Marek's, worm problem, respiratory disease, ect. After 2 dead, 3 still sick and being treated, 2 wks later I got a partial necropsy report that said they were full of several kinds of worms, Coccidiosis, and further testing was being done to diagnose if they had Marek's or Lymphoma, haven't found that out yet. I was told that chickens don't get colds, they get respiratory infections. While I treated my cockerel with Tetracycline, ACV (4 TBS per gal), yougart and electrolytes (cause he wouldn't eat or drink, had to give it to him by hand in a syringe without a needle daily), he is fully recovered from the sickness and shows no signs of being sick, except that I found a worm in his cage (tape, I think) he has never been wormed, but he was not in with the new pullets we just aquired 2 wks ago, that started all of this. He was born and raised here and always free ranged, and never been sick at all, until these new ones were brought here. So in conclusion, I would keep a close eye on them because I don't think they just start sneezing if there's not somethink going on. Just my opinion. Also Tetracycline is about $8.00 a 6.4oz bag, and a little goes a long way (2 teasp. per gal water), and can be found at most feed stores. Don't let symptoms get bad before you start to treat though. Could be worms, have they been wormed?