When it comes to steak, the muscle fibers of the meat are usually clear of bacteria and other pathogens due to how it's structured. Usually, if there is any bad bacteria or pathogens it's on the very outside of the steak itself. As long as the outside is cooked the inside can remain partially uncooked, while still being safe to eat. Something like chicken, on the other hand, is absolutely not safe to eat undercooked. This is due to the shape of the muscle fibers which allows bacteria and pathogens to permeate inside of the meat itself.
