Food Pre-Packaged in Vacuum Bags I often purchase chicken and fish that have been vacuum packed at the factory. Is the food, never having been exposed to air, susceptible to botulism or other anaerobic organisms? Is it best to sous vide these in their frozen state?
I wouldn't advice either one.

If you sous vide from frozen, your cooking times are going to be off.  You might end up with it undercooked in the middle unless you significantly increase the cooking time.

And I've only done it in the packaging once.  Never again, as there was little to no flavor to it.  (no browning, no seasoning).  The only time that I might be willing to re-try it would be if I went to the partially-prepared section, and got the ones with marinade already in the bag.