I had just posted my reply to Amy Z for her FIP question, but to make a long story short, we lost our 6 mo old feral kitten to FIP last month. We didn't even know she had it until she had her spaying (there was fluid in her belly). She died 2 weeks later. I'm pretty sure the surgery probably exacerbated it and accelerated it. I have a collie who had demodetic mange (an auto-immune disorder) that was severely compromised by her spaying and it took us a year to get it back under control. If we hadn't spayed her, lord knows if the kitten would have died so soon. There are plenty of cats that live with it. Besides the fluid in the belly, some other characteristics are golden urine (and I mean GOLDEN) and a yellowish tint to the inside of the ears. I never did see the ear thing on Cleo, but her urine did turn golden.
It's very frustrating as is TB in humans. You can test positive for TB, but it only measures exposure not actual illness. I won't have my other cats tested because it would be inconclusive, a waste of money and nasty for them. Try to keep your cat healthy in the meantime! Good luck!