The vast majority of fish will test positive for tuberculosis, including wild ones, but that has more to do with the testing process than whether or not they actively, actually "have it." At issue is that the there are several related bacteria of the genera Mycobacterium, including M. marinum ("fish TB"), and -- of course, Mycobacterium tuberculosis, which is people TB. Basically, fish exposed to any of about 20 different species of bacteria will test positive. Of these diseases, the only one that is of any big concern is M. marinum. As an aside, at least three other members of the genus have been shown to be able to infect both people and humans, but they're not of particular concern.
Like a lot of diseases, you have to have high densities of the bacteria growing to have a realistic chance of being infected -- fish or people. This is why we believe its fairly common in commercial facilities: fish are crowded, conditions are bad, basically 1849 San Francisco, or 1912 Europe. So, diseases are a huge issue, and this is one that does show up. However, when moved to clean, healthy, less stressed conditions, most fish are able to fight it off, and it isn't a big concern. This is one of the earliest described fish diseases, and it really isn't mentioned in the literature much: it just isn't a big killer of fish.
Of course, that's not why you're asking "should it be a direct concern." M. marinum is one of the very few diseases that can make the jump from fish to people. I've had it -- twice. It isn't particularly fun, but it is easily treated, and most of the stuff you read on the internet about flesh eating, cripping pain is bunk - it hurts, and you're going to spend a good month on antibiotics, but you're not going to be crippled or have your skin peel off or get freeze therapy.
With that said, infection rates are incredibly, incredibly low among aquarists. Seriously, when you figure out the number of aquarists and the number of cases per year, you're more likely to be struck by lightning while winning a scratcher than you are to get it (why doesn't my luck ever hold for the GOOD stuff?) You can prevent infection pretty easily -- don't get jabbed by your fish's spines, don't go into the tank with open scrapes, cuts, etc., and use some sanitizer on your hands when you get done, as well as washing afterwards.
Oh, and for real fun, you'll fail TB tests after getting it. :-/
