Ohhhh. The ghosts only mess with you if you haven't seen the mold, because they want people to get rid of it. And this manifests after a certain time (instead of a certain amount of mold) because it's not a property of the mold, it's a reaction to it.
I like it. It's simple, and there's nothing wrong with that. The spores growing in one researcher's home, presumably to live off of ghosts that follow him around, was a nice touch.
Now I'm wondering if ghosts are a renewable resource. If the Foundation successfully prevents any more deaths at this thing's containment facility, will the mold eventually consume all the ghosts it can reach from there? If so… what happens then? o.o
(There are several other articles that refer to Site-44, mostly in ways that aren't compatible with this article's description… but a cursory search for other site designations indicates that this is hardly unusual. Up to you if you want to change it.)