I don't have any evidence to back that up, nor am I expert on the topic. But I find that dirt (and outside shoes) is usually fine, you will find more dangerous

I don't have any evidence to back that up, nor am I expert on the topic. But I find that dirt (and outside shoes) is usually fine, you will find more dangerous bacteria in door knobs, coins, etc. Basically everything your hand touches has a higher risk of getting you sick. That doesn't hide the fact that having a dirty floor looks gross though, from a aesthetic standpoint