chix: contagious yes, very much so, but... to other cats.
I used to spend my time at a humane society, and they had their signs and measures to prevent spreading desease from cat to cat, a URI being one of their top priorities.
At this place... if a uri spred to to many cats... at one time... and quaranteen/meds for a few didn't help... they would put them all down.
There would often be times I would come into work and the cat section would be closed down, all dark, they were all gone.
Very much sad.