Originally Posted by Yakk

If you want to make safe rare hamburger at home, do the following:

Get a trusted butcher, who knows you will be eating some of the meat rare. Have them cut you some steaks.

Cook the steaks 'blue' -- sear the outside (all sides), killing any surface bacterea, but leave the insides raw. The thicker the cut, the more rare meat.

Now, using a clean meat grinder, grind the meat. You can choose to cut off the seared outside of the meat before grinding, in order to make the meat even rarer, or you can just grind the seared meat with the raw insides.

Make hamburgers, cook rare. (see above)

There is a high-end restaurant that does rare hamburgers like this back in my old home town.

The only danger here is that the meat was penetrated/pierced during butchering. Hence the trusted butcher.

Admittedly, human beings are pretty good at defeating invading organisms, so avoiding this level of care isn't as dangerous as say, high blood pressure, or a 40"+ waistline. =)