fruited sour carbing

You purposely infected it with either dregs or commercial bugs/bacteria. These strains have usually been artificially selected for their ability to dominate in wort, so I wouldn't worry about an "infection" because the bugs you pitched should dominate any wild bugs that might try to cause an infection and probably destroy them. Not really sure what @ssam meant by that statement though.

 

Sure, what @DrMindbender said. You infected it on purpose. I didn't mean anything other than that. It was a little joke.

That said, beer is most resistant to infection if its hopped, fermented, and carbonated. Hops are naturally antimicrobial; alcohol too; and carbonation lowers pH. You may not have much CO2 yet, but your beer is certainly hardy enough to ward off an [unwanted] infection provided you adhere to best practice sanitation techniques.