Can I cure the Sims affected by the Mother Plant w/o playing Strangerville again

FlamingoKicker​   The reason you are getting infected sims in a new game but haven't been to Strangerville is because the story is active and there are several infected sims out of the box.  To get rid of the infection, you'll have to play through the Strangerville story once.  Once you defeat the motherplant the first time, every sim that is infected will be cured and you'll never see infected sims again unless you activate the story again.  Just don't use the option on the motherplant to reactive it.

Hope this helps.