hey there!
mycobacterium is one of those bugs that can be found pretty much anywhere. It's in dirt, moist places, etc. It can commonly be found in improperly cleaned medical devices, too. Do you know what the bacteria actually is? AFB mycobacteria can be MAC (mycobacterium avium complex), Mycobacterium abscessus, and a few others. M. abscessus is the more difficult one to treat. I've culutred that off and on for about 4 years now (maybe more). I am currently being treated for it as it's started causing me a lot of problems (fevers, shortness of breath, tiredness). I've been on IVs for it for the last 6 months. I was treated for MAC about 5 years ago and I haven't cultured it since.
I won't lie or sugar coat it for you. It can be treated, but the treatment course can be long and daunting. If it's MAC, a long course of oral abx can do the trick. If it's something else, like M. abscessus, IVs/nebs are often the only choice as it's a pretty tough bug. That's why I've been on IVs for so long, too. You'll have to wait it out and see, and talk with the doc, though. I've met CFers who culture M. abscessus and it's never treated simply because it doesn't give them any problems.
Good luck and let us know how things go!