Well, in the technical sense, our kids DO have a "brittle" condition-- that is, one which can be acutely life-threatening within seconds/minutes and without warning in a "normal" setting that poses no risk at all to other people without their medical condition.
That pretty much defines "medically fragile."
The same thing could be said about a particular child with a seizure disorder or diabetes-- thought probably not ALL children with those conditions. Similarly, however, not ALL people with food allergies live with that kind of low threshold and rapid reactivity, either. It wouldn't be fair to apply that terminology to someone who doesn't react discernably to cross-contamination. KWIM?
I have applied the term "medically fragile" to my child in advocacy work on her behalf. Because it's true. And yes, I've had experience with conditions/children who would generally be considered that way (CP, extreme preemies, etc.). The thing is, when you break it down, there are a lot more similarities than differences. We plan our lives around FA to exactly the same degree and in many of the same WAYS that my sister did for four years after my nephews were born at 24 weeks gestation.