Post-apocalyptic movie?

I've seen a bunch of reviews that mention that this movie takes place in a post-apocalyptic world.

I'm guessing it must have been an epidemic of some kind considering that all the infrastructure seems to be intact.

If that's the case, it's sort of refreshing for a movie from the 80's considering that in a lot of post-apocalyptic movies, it was caused by a nuclear holocaust. If it took place in an alternate timeline where a nuclear war occurred in the 60's, they would have still been rebuilding and trying to restore the basics like farming.