hamburger ???

Yes, you definitely can. You can cook hamburgers sous vide at 131°F for few hours for medium-rare or 140°F for medium For some more information you can read this article from Serious Eats

You certainly can, and I do regularly. It is worth pointing out that 70c is actually a lot higher than required to be safe. Much lower temperatures above around 55 deg c will actually pasteurize the meat. It won't be sterile, but bacteria is reduced to safe levels. For times required, refer to this site or douglas baldwin.

The answer to that question for me is yes of course....Most things can be cooked sous vide method the result is dependant on the time, the product you are cooking and the method you are using to cook under vaccuum.

if you are cooking an item such as a burger, things to consider..

is my burger made from prime clean beef and there fore can this be cooked under well done with an internal temprature of less than 70c and be safe

or is my burger a mixture of beef and therefore needs to be cooked to 74c and above to kill all pathogens.

Cooking sous vide style in a water bath creates an environment that bacteria love due to the nice cozy ward temperatures they love to multiply in and as the proteins do not metabolise.

If nothing else just make sure you cook your food to the correct internal temperature so you dont make yourself sick

aaron