Everything epgui said above. Just to add another line of argument: thanks to sequencing, we also know there are a lot of germs that we simply can't culture. We

Everything epgui said above. Just to add another line of argument: thanks to sequencing, we also know there are a lot of germs that we simply can't culture. We used to suspect that, but now we know that. Most general hygiene methods are non-discriminitive, so as cleanliness goes up, opportune exposures to rare edge cases go down, and probably go down fast. We are becoming, in a sense, a species of oligoculture hosts.