It might be worth noting why even your doctor can't answer such a question with great accuracy: "infection" covers a huge range of possibilities in terms of organisms. It could be, and probably is, Escherichia coli or possibly a species of Staphylococcus, but it could also be Neisseria gonorrheae, which causes urethritis but is an entirely different kettle of fish.
Note that there's a difference between "could have" and "would have". It is never, ever possible to determine with certainty what "would have" happened under other circumstances. It's often possible to make educated guesses about what "could have" happened.
I'm curious how you fear you might catch something with "penetration" (I'm assuming vaginal). You would have worn a condom, right? How are bacteria (which are to viruses as skyscrapers are to cars) going to get through latex that can stop HIV?
Although nothing's certain without a culture, statistically, a large majority of young women with typical "UTI" symptoms do, in fact, have lower urinary tract infections, almost always with E. coli. It is statistically unlikely to contract an oral or male urethral infection from sexual contact with women with common UTI's. If you have ever had unprotected oral or vaginal sex, you have almost certainly at some point done so with a woman with a UTI. In other words, the scenario you mention (SP has a UTI, doesn't tell you, you go down on her) is almost guaranteed to have happened to you already if you make a habit of performing oral sex on SP's.
I'm not really sure I'd want to rely on the self-diagnosis of a stranger in any event, for either presence of or absence of infectious illness.
