Ground meat is only dangerous if it's been sitting. Beef is perfectly safe to serve at rare if it's been ground the day of serving. Personally I think medium is the absolute minimum, not because safety concerns, but more because burger falls apart more easily the less it's cooked.
> Beef is perfectly safe to serve at rare if it's been ground the day of serving
Why would that be the case?
The reason we can cook and eat steaks rare is because dangerous bacteria form on the outside surface of the steak, and cooking the outside while leaving the inside rare destroys the bacteria. Grinding the beef mixes the surface of the beef with the inside, meaning you should cook the inside to 165F as well.
Beef before it's cut has the potential to have harmful microbes on it's surface, but they don't travel very fast, so they can't get deep, which is why it's safer to cook to a lesser degree than ground meat.
Ground meat on the other hand can introduce those harmful surface microbes to the rest of the meat, so burgers have to be cooked all the way through to ensure those microbes are successfully deaded.
