Cleaning outhouse produces 5kg of dirt with food poisoning

I believe this is indeed intended behaviour - I think the cause for this is the dupe gets contaminated (i.e., they get their hands dirty) from cleaning the outhouse and this causes the contamination of the normal dirt.

The 5 Fs of Field Sanitation:
Flies, Feces, Foods, Fluids, Fingers.

The game has 4 of them, but these are vectors for the spread of germs. Don't be surprised that germs spread on these vectors. In this case Feces -> Fingers -> Foods is a vector you are experiencing.

I would agree with the fact that if the dirt is taken from the outhouse it should have food poisoning. I would however consider it to be polluted dirt. As in real life you would never get "clean" dirt from a used outhouse. all the dirt should be polluted. 

The problem with the implementation is that you cannot choice how this dirt is treated.  In real life you would be able to decide how to treat the dirt taking germs in consideration. In this game however the decision what to use were is not made by you, it is made by the game. and for the game dirt is dirt with or without food poisoning. And it freely uses it for any application where dirt is used. 

As the outhouses are the only toilets available in the beginning of the game there is no way to prevent the creation of this dirt with food poisoning. and if you still use meal wood when the outhouses are being cleaned there is NO option to prevent the dirt from being used. and washing hands does not change the food poisoning on the dirt. 

Requiring an ore scrubber with chlorine for a starting base is not an option. 

I really believe that this implementation is not beneficial the the game mechanics.