Also be aware that you can't actually make significant progress in the mystery unless you use the Aspiration that came with Strangerville. So don't give any sims that aspiration, and you should be (mostly) fine.
Played Infected sims are infected for a 3 hour period, that I think is supposed to be 1 Am to 4 Am, but it's been a while since I've played through. And they wake with all their needs filled. NPC infection periods are more random, it appears, though they're *also* infected for the time Played sims are infected.
I have had infected NPC (as opposed to generated townie) sims show up at festivals in San Myshuno, but they're not usually seen wandering outside Strangerville very often.
Also I know you said realistic gameplay, so this may not be an issue, but if you have Vampires and a vampire drinks from an infected sim, they get infected.
