I would call the vet and ask, as they will have the best idea of how severe they felt this is, along with if it's contagious. I would keep them seperated for sure while you are seeing symptoms.
Re the eating...its possible your kitty's sense of smell is off due to this uri. Try gently heating the food, try really strong, fishy cat food, try human baby food meat (just check label to be sure there is no onion in it)...gerber second stages is one brand. An easy way to boost your kitty a bit is to get a tube of Nutri-Cal - a high calorie paste that you can gently put on their lips to get them to lick it off, or see if they will lick it off your finger.
Try warm, plain chicken broth (just boil up a chicken thigh or wings with skin on, strain and serve the slightly warm broth)....if your kitty is drinking well, try taking a pate/ground food, mixing it with warm water, blenderizing it, and see if they will lap that up.
I wish your kitty all the best - do call, your vet may want to see your kitty again.