Lisa,
I have two daughters, and a nephew, who all have CF. I do not keep my girls away from each other, only away from their cousin.
Some books/doctors may tell you to have the siblings do their CPT and nebs in seperate rooms, but I just find that too difficult. My kids both want me to sit with them while doing treatments, and I can't be in two rooms at one time. They are only 18 months apart, and how do you keep two little kids away from each other? Not possible, at least when they were little. Even now, they are each others favorite playmate (even though the argue a lot<img src="i/expressions/face-icon-small-smile.gif" border="0">)
I had always assumed that what one would culture, the other would too. But that has not been the case. When they were little, they both would catch things like strep throat at the same time. But maybe that would be because I would catch them drinking out of the wrong cups or taking their sisters binkies<img src="i/expressions/face-icon-small-smile.gif" border="0"> and plopping it in their own mouths! Now that they are older, they know not to drink or eat after the other one. If they are coughing, they know how important it is to stay away from their sister.
Hannah started culturing PA about two years ago (has since had almost a year of clear cultures of PA) and I thought that Kayla would absolutely start culturing it. That worried me a lot, especially b/c Kayla seems to have more lung issues than Hannah. But, she never has cultured it (knock on wood). Both girls culture MRSA and Staph, but only one the PA. I will not say that it is not growing deep in there and not showing up, but as of now, there are no signs of it.
There are many parents on this forum that have many children with CF, and you will probably get many different ideas on this. But, for us, our CF doctor has never told me to keep my girls away from one another. Only a distance from their cousin with CF.
By the way, Toby is a real doll<img src="i/expressions/face-icon-small-smile.gif" border="0">