(spoiler) Make sure you have a really cheap refrigerator when moving in a new neighborhood.

Is this something that will happen as soon as you move into the neighbourhood, like any regular welcoming party?
Or is it something that only happens if you begin the storyline?
I am asking, because I was under the impression that the infected Sims would be a minimal occurrence if you didn't initiate an investigation.
But if these types of Sims are in the welcoming party I am forever turned off, unless there is a future patch to disable the "strangeness".