Serious Eats - seriouseats.com

I would STRONGLY advise against ordering burgers with pink middles. This is a great way to get sick and possibly even die. A friend of mine ate an undercooked burger, got a rarer (1/100 chances) form of E. Coli poisoning, which when treated by the traditional method causes all the E. Coli cells to burst at once releasing a fatal dose of poisons. Fortunately, they recognised it was happening early enough to prevent his death, but there is no way to differentiate between the two forms of E. Coli until you start having serious complications with the treatment. A hamburger can get contaminated when the meat is ground up and some of the feces or stomach is also ground up with it (gross I know). Since the meat is ground up, even the middle of a burger needs to be fully cooked to be safe (unlike unground meat like a steak). Please take care... a burger can still be really juicy and cooked properly.