I've been asking myself the same thing, Saito. I've been asking it a lot. And in the GM chat.
Anyway, word of god is word of god but just as an fyi, I don't recall healing kido being able to cure diseases in canon. Even in theory, it doesn't work since the spell works by healing the reiatsu of the patient, then supplying more which does nothing to a pathogen. If it were able to be healed with kaido, it can't be a bacteria unless the body can just naturally and easily fight it off on its own and the bacteria is so weak that it is contingent upon the other person's body being strained and dying to do anything. As far as I'm concerned, it is Ganryu's ability so he can do what he wants but I'm clarifying that in general, it doesn't work and that if he wants it that way, I'll suggest some clauses to the mechanic to make it make sense.