Actually quite harmless, perhaps offensive if strong enough and not getting used to it.
The second worse problem tollerating rodent to free run a house, Chew destruction is number one.
My grandmother was one to let house mice stay, even feeding them treats like little pets.
Upstairs where they seem to nest, you could tell the rodent urine, not much offensive but just devastated a sock drawer for nest. That was a bit strong. Mice mark by peeing, and hard to clean after. the dirt, just sweep up and dispose, wash hands after handling anything soiled you are good to go.
You can buy products at many pet stores to deal with odors, small animal odor-b-gone, gell beads etc.
True HEPA air filters trap bacteria and odors.
Things I use for my pet rodents and just not offensive.
Best solution ever for rodent problems are those electronic rodent repellers, they work, no poisons,traps or dead mice, just no mice.
No current issue with Hanta, that was restricted to two north central states, Pet rat Hanta in the south west, now under control.
Worst from house mice is possible mites or lice that can vector to humans and hat is a bit rare.