[Kiani]

If the burger is made out of mince it should always be cooked right through, reason is that mince is a group of smaller particles of meat, rather than one piece off one part of one animal. All meat contains food poisoning bactiera but majority of it is killed through cooking, leaving only trace amounts that we have in our bodies anyway. In one pice of meat its fine to leave it slightly uncooked as bascteria usually live on the outside of meat. Mince burgers however, each little piece of mince contains the bactieria and each little piece needs to be cooked through, as due to the consistancy of mince, the bacteria also live on the inside of the burgers.

Im not sure about anywhere else but I know that in Australia serving bugers made of mince anything less than well done is a breech of food safety pactices for this very reason.