It turns out that my fosters had an upper respiratory infection- so, today I
had to turn them over to the SPCA to get put down. If treated, it could
have been a total cure or someone could have a sickly cat for the rest of
their lives.

I don't understand. They just needed antibiotics. All of my fosters cats and
kittens had URI. I just gave them clavamox and they were all fine in a few
days. None were sickly forever. Am I missing something here?