Hi there K,
To my understanding, it is not a problem for a while. The new lungs won't have the CF faulty genes in them. However over time (we're talking years here probably) as the lungs take any damage and need to repair, I think those genes in the new lungs, will get replaced by CF genes. If this makes sense?
People post transplant can still get infections, same as anyone else, especially with the strong anti-rejection drugs that can cause a weakened immune system. But, they will no longer get CF infections.
Wowie, that's a hard one too explain