Cast iron is the original non-stick cookware. Every once in a while, you season it. Heating the iron opens its pores and allowing the oil used in the seasoning to be absorbed into those pores and keep it non-stick.
So not much is really sticking to it to begin with. But the point of the story is this: If you really feel like you need to scrub it with soap, you can, AND you can re-season it easily. (Oven on 225 for two hours after coating the skillet with veg. oil or lard).
On the other hand, if you are trusting that the skillet is hot enough to cook your food to a safe consumption temperature, than any of those “germs” on the food to begin with that may remain on the skillet have also been rendered harmless. Water and elbow grease get off anything additional.
So, you don’t need to worry one way or the other. . . . either you are going to be doing alot of skillet seasoning, or you will get comfortable knowing that it’s safe not to use soap often.
And trust me, if there were a danger, the company wouldn’t recommend it. The last thing a company wants is for you to get e.coli because they told you not to clean their wares appropriately…