It’s called toilet plume.
A toilet plume is the invisible to the naked eye, cloud-like dispersal of raw, infectious sewage particles as a result of flushing a toilet. Flush particles rapidly rise out of the bowl and several feet into the air after flushing. Aerosolized droplets can remain suspended in the air for tens of minutes between users, posing an inhalation risk. These invisible particles go on to coat and spread onto surfaces like floors and counters or objects like hand towels, bathmats, or even toothbrushes.
I’ve put the toilet lid down since that mythbusters episode where they examined how much fecal matter got onto toothbrushes that are in the same room as the toilet.
Now my toothbrush isn’t in the same room as my toilet but I still shut the lid.
Spoiler for the mythbusters episode… It was a lot of fecal matter… A lot.