This is a very difficult position to be in. Those numbers are certainly well within the negative range. However, who did the test? If this is a ped or unaccredited clinic, I'd have doubts that it was done properly. Did they get enough seat? Was the sweat diluted? So many factors come into play here.
I'm having a hard time getting past the psuedo that he's culturing. However, reading back, I think you mentioned he has a trachea, and I know that there is a lot of mucus production with those. I'm thinking that it may be possible for the pseudo to take up residence in the trachea like it would in a set of CF lungs. I still feel that the meds they are trying to treat it with may not be adequate.
I hate to think that a child may not get the proper testing/care, simply because the state is paying for the medical care, and won't approve him being seen by an accredited facility. I've seen this happen in my own state, and in my own family. <img src="i/expressions/face-icon-small-sad.gif" border="0">
Stacey