Ask your vet why he/she doesn't want to use enroflaxin and why he/she chose not to perform a culture.

It is extremely uncommon for a URI to be viral. Bump your temps up (I'd go 86-88 on the cool side, and 95 on the warm while treating the RI) and find a vet that will do a culture to determine how best to fight the infection.

Hope this helps.

-adam