I know a few members are keen on 'rare hamburgers', something which I don't find appealing
and came across this article on the subject.
---

3. Rare meat
When cooking and reheating meat, there are some simple rules to follow. Whole pieces of meat muscle such as steak,
pork and lamb can be cooked on the outside, say barbequed or pan fried, so they're still rare on the inside.
Historically, under-cooked pork has been feared due to a parasitic worm, but this has never been seen in Australian pigs.
Poultry and all minced, rolled, stuffed, tenderised and similar types of meat (including burgers) need to be cooked right through.
This difference relates to where microorganisms are found on the meat.
We know microorganisms live on the surface of raw meat because animals naturally harbour microorganisms.
That's why just cooking the surface of a whole piece of muscle meat is sufficient (excluding poultry), because that will kill
any potentially harmful bacteria.
When that meat is minced, rolled, stuffed, mechanically tenderised or turned into patties or sausages, the surface of the
meat and what it's carrying is then mixed through the whole product.
It's also possible for chicken tissue to be colonised by bacteria (which just doesn't happen with other animal meat types).
That's why these types of meat products need to be cooked through to the centre.
It's a 3 part article and the balance is here