One of the first sure signs of an animal getting better is by seeing how much water and food they are eating and drinking. There would also be the cold nose theory, and the use of the litter box.
I would recommend that you take the kitty to the vet if your kitty is sneezing a lot, and has shortness of breath, this could be a sign of feline lukemia, and this isn't a good condition for them to have, it's usually fatal. Hope this helps. Good luck.

 Well they will generally look healthier! They will definitely have a bigger appetite! And usually be a lot cleaner!