Deb - don't worry and don't blame yourself. If Dylan wasn't showing any signs your vet would have never caught it back in Dec. or probably even a month ago. As long as Dylan, and Eliot, are eating and drinking they will be okay. The main thing is you now know and they are being treated. Those antibiotics do wonders but you know that. Look at how well Emily is already.

Ripley caught Jazz's URI but didn't get sick until 6-8 weeks after we brought her home. By the time I realized he wasn't eating and drinking he was a very sick kitty. The vet told me he had probably had it for some time but didn't show it until dehydration set in. I felt so bad but my vet reassured me it was easily missed because they hide their pain and illness so well.

I bet once Dylan is fully over this you will see a more active cat. That is what happened with Ripley. He was more playful than he'd been in years.