Sous Vide Pasteurization
I mentioned this a few times in the Whole Turkey recipe/guide, but I found a great table that really boils it down.
Here's the concern; you can use the Sous Vide to get really low temps and cook the meat just perfectly tender; however, if you go to low, you're actually encouraging the growth of certain bacteria.
This is a table of temperatures and acidity that promote bacterial growth.
You'll notice that some of these bacteria can grow even up to 126 degrees Fahrenheit.
However, most have optimal growth rates between 80 and 110 degrees (like Botulinum), and during their growth can produce toxins which cause food poisoning. This is why thawing meats in hot water is not recommended.
Salmonella is the most resistant to heat, so by targeting Salmonella with pasteurization temps and times, you're able to clear out most of the other baddies.
Taken from Understanding Food Safety – Stefan's Gourmet Blog
Different bacteria are more common on different meats, which is why different kinds of meat have different Pasteurization times, and is broadly discussed on this great site:
A Practical Guide to Sous Vide Cooking