I cultured it once pre-transplant and then never again. They tell me that it just didn't colonize. If his sister only cultured it once, then maybe it never colonized, but like Mel said, if she's been culturing it over and over again since she was 2, I would think she is colonized with it and still has it.
I hope your hubby is like I was and it only shows up in the one culture, then no more. Good luck!