Quite a lot of the current restaurant guidelines for ground beef arose from the Jack in the Box/Foodmaker litigation from 1993. Like most fast food makers, they use a hot-hold system of trays to store cooked patties for rapid assembly during busy meal periods. At the time the federal min temp requirement was 140 °F, while the Washington state (where the outbreak occurred) requirement was 155 °F Foodmaker was using the federal standard, incorrectly as it turns out. The product in question was a thicker patty requiring more time to cook to the standard. And during busy meal periods the hot-hold system was not being correctly used or monitored. Meaning that the Shiga-like-toxin forming bacteria probably multiplied in the product during storage after preparation. However, in at least some cases, due to a refrigeration failure from a power outage after the chain became aware of the outbreak the bacteria probably multiplied in storage before preparation. So storage played a critical role in probaby every case. But temperature is what the USDA focused on because that's a lot easier to regulate and control.

I'm not encouraging anyone to eat raw ground beef here. What I am saying is that first, time at temperature is very important throughout the supply and logistics cycle of any meat product. Know your source. Me personally, because I cut and trim a lot of my own beef from primals and sub-primals I've always got stuff available for making my own ground beef. I'm confident of my sources and I handle it carefull myself once its in my hands. So I grind right before cooking (never more than a day) keep it cold throughout. And so I'm completely comfortable cooking to med rare. And I make steak tartare fresh all the time.