This chart helps explain about the required times at various temperatures to kill bacteria sufficiently for FDA guidelines.

For example, if you get a piece of meat up to 165 degrees for a 15 seconds the food is safe.
If you get that same piece of meat up to 140 degrees for 35 minutes it is the same as 165 degrees at higher temp
Or if you cook (poultry) at 135 for 80 minutes it is the same.

The principle around Sous Vide is cooking things at a low enough temperature for long enough to kill the bacteria. My father-in-law was a nationally recognized researcher and expert in e Coli so my wife has been very exacting about cooking meats safely. Eating chicken and pork for her cooked via Sous Vide at a lower temperature than 165 when it is still pinkish - was a bit difficult for her given that she was so paranoid about getting the meat temperature high enough.

This is why sous vide is a very safe way to cook - even though it might not look done enough.