[user104658]

If you live anywhere vaguely rural there are mice under your house. There just... definitely are. All you can do is B) not leave out any food sources and B) block any entry points as well as you can to stop them coming in.

And if you live in a city you almost certainly have a rat or 5 living somewhere very nearby. You just don't see 'em.

Be careful if you need to dispose of them and wash hands thoroughly and you'll be fine. Just being "near" one isn't going to do anything. Little cat we had a few years ago was an absolute monster of a hunter, brought mice in (living, dead or somewhere in between) almost every night in summer. Also the occasional frog .

Was CONSTANTLY cleaning mouse blood & guts off the hall floor . And had to catch & release loads that she brought in alive .

Speaking of which.

Just having a cat will often keep mice out of your home. The mice can smell them and are smart enough to stay away. We have a little house cat now (Ragdoll) and she would 100% not be able to kill a mouse, but they still stay away because they don't know about her gross incompetence.