They do live in a controlled environment. And this is a reference hospital for infection control. I know a nurse who was once one in charge of infection control in the child’s ward — actually, a smaller hospital of its own in the main hospital grounds; the whole thing is huge — and she was quite competent, as are most of the medical staff there. They usually go to conferences in the US and Europe and all that.

I believe the author refers to the danger of infecting others.