Zoonoses

How common is it for cats to get upper respiratory viruses from their owners? I know that in theory it's possible but I don't know if it's something that happens much in practice. I usually don't worry about this--in fact I can't remember it ever happening with my cats--but right now I do have a cat with some medical issues, so I really don't want to give her something else.

I don't think it's very possible at all, unless it's some weird strain.  However, stress can induce a lot of health issues in cats, including upper respiratory infections.  Calming agents can help keep stress low and help out overall.

As a matter of fact, it is literally impossible for a cat to catch a human cold, and vice versa.

This was discussed at a symposium I attended several weekends back, at U.C. Davis Veterinary Teaching School, some of the best educators were giving lectures on many different things, and this was a topic of discussion as well.

There is no way possible to get or give a virus to your pet.

There have been a few very rare cases: , e.g. H1N1:
The Cat Who Got Swine Flu

Can you really give your dog or cat the flu?

Pets May Get the Flu More Often than Thought

Something more scholarly from the CDC: Influenza A Pandemic (H1N1) 2009 Virus Infection in Domestic Cat

From the NIH: Serologic Evidence of Pandemic Influenza Virus H1N1 2009 Infection in Cats in China

I did a presentation on the Flu Epidemic of 1918 and the possibility of another and I found that info about a bird flu that became contagious among cats.  What I found, it was first found in tigers in a sanctuary and they checked whether it had become contagious among cats with domestic cats and it had.  They routinely have a tiger here and there die of it at the sanctuary because of eating contaminated poultry.  They had a number of tigers get sick at once which is why they thought it had become contagious. 

Interesting information, thank you.

While the transmission of H1N1 virus may be possible in very rare instances, I think it's safe to say to the OP that he doesn't need to worry about giving his cold to his cat.

I also can't help but think that, while the cat was strictly an indoor cat, there are viruses that are hearty, living in the grass for instance, where someone can walk on it and track the virus into their home.

Like panleukopenia for example.

While there are a few suspected cases there is no confirmation that gives concrete evidence that a mutated strain exists. 

Who knows someday, as some viruses have such a capacity to adjust themselves to survive in hosts, I certainly hope not...but I would say overall, not to worry about your cat getting sick.

Exactly why my vet recommends vaccinating indoor cats.

Exactly!

However it is no longer recommended to vaccinate cats yearly, at a maximum every 3 years.

Some old school vets are slow to adapt to this. Overvaccinating is dangerous too.