When do Feverish Citizens spawn when the Swamp Fever World Change is not active?

Question

I know when Swamp Fever is active the Feverish Citizens have a chance to spawn every 30 minutes after server save. Apparently they do have a low chance to spawn even if enough Medicine Pouches have been handed in to prevent Swamp Fever.

When the Swamp Fever World Change is not active do they still only have a chance to spawn every 30 minutes or is it completely random?

Answer 1

yes

minimum eighty characters must be used to answer so i have to write eighty characters

Comments

"yes"?  Could you elaborate more, please?