They are probably looking for radioactive material to make a dirty bomb out of.
At this point your guesses are as good as any. I have no clue about what is going on, but I do know this: something is going on, and it's affecting all the hospitals in Illinois.
Could be anything, could even be a training drill for all I know. But, (in the words of Tony Soprano) irregardless, something is going on, and I hope that FRland can help figure that out.