Costco blade tenderizes its steaks. The label says so, and it's the reason a Costco steak comes with a cooking temperature printed on it. Before the steak hits the case it goes through a machine that pushes rows of thin blades into the meat to cut the muscle fibers, so a Choice steak eats more tender than it would on its own. You can't see the cuts once it's done, except sometimes in the fat on a ribeye. The catch is what rides in on the blades. E. coli lives on the outside of a cut of beef, which is why a rare steak is normally safe. The sear kills what's on the surface and the inside was never exposed. Push that surface into the middle with a blade and rare isn't safe anymore. That's why USDA says a mechanically tenderized steak gets cooked to 145F with a 3 minute rest, the same number as a pork chop, where a steak that wasn't tenderized carries no cooking instruction at all. USDA figures about 11% of the beef sold in the US is mechanically tenderized, and since 2016 the words have to be on the label. Costco started printing them in 2012, after an E. coli outbreak in Canada was traced to its blade tenderized steaks. The ground beef isn't tenderized. If the package in your cart says blade tenderized or mechanically tenderized, cook it through.