If the burger meat is ground on the restaurant premise and kept cold, order it as rare as you want.
The chances of getting sick are pretty much nill. The media has hyped it up way worse than it is.
Simple research on the net will give you all the REAL information you need. Grind your own burger and eat it the way you want and STOP STOP STOP worrying. Same goes with eggs, etc.
A poster said a big truth, if the meat is fatty enough 20-25%, even a well done will be juicy and flavorful. Just be sure to never ever press the cooking patty.