One easy way to deal with it, and most obvious way is to finding the source and killing it by doing the storyline.
I don't have strangerville and what i've seen isn't enough to convince me to buy it at any point either, but when you got a pandemic, you got to isolate the outbreak and deal with it or it will start spreading, in the sense of realism plays: it is accurate to expect sims all over to get infected when there are infected sims nearby handling food, chatting, hugging others and so forth when there is nothing to contain it.
So even if i had this pack, i wouldn't consider it outside the realm of possibilities.