I really couldn't say as I have never had to deal with a URI (knock on wood) but I guess anything if sever enough and it goes untreated can be deadly. I don't know if I have hear of it and there have been some pretty bad cases that I know of but with an agressive course of antibiotics and TLC they have all pulled through. I am not sure about the scratch though. It could be because the system is so low due to being sick that the body just can't heal it at a normal rate.

All fingers, toes, paws and whiskers crossed here for the little ones. Sending them prayers and good vibes from Italy.