Find a local farmer whose meat handling you trust to reduce the likelihood of contamination.

Otherwise, get a steak, wipe it with an ammonia solution, rinse it, and grind it up yourself. The E.Coli, if it exists, is going to be on the outside of the steak; the ammonia wash will kill the vast majority of it, and you get the benefit of fresher hamburger.

Alternatively, freeze your steak by dipping it in liquid nitrogen. A normal freezer isn't sufficient to kill E.Coli, but a liquid nitrogen dip will do the job. :)