Now if I could just get the cat to wipe her feet.
As for the cat...
It's a disinfection mat inside the grey wrapping, placed in a waterproof tray near the door, and is usually soaked with water and a disinfectant(usually a natural one, for general use). A large piece of disinfectant-soaked packaging foam in a tray, can be a DIY solution to it, too. Cats usually avoid sidewalks, and don't usually make it to the nasty city streets.... trees and grass being their norm. So, this might be somewhat extreme ... ;^)
But I live in the country and her paws never touch concrete - or other man contaminated surfaces. The yard and woods do have some germs, but for the most part, the rains and sun washes them away or disinfects them.
Besides, I have a cat that would never, but never, set paw on that. She would hop over or never go out...or once out, never come in. (and I have the world's most skittish cat - she had a really hard life before coming here and so, even though she's all over my lap and keyboard and snuggles up close as she can at night...there's no way I could get a hold on her near the door, knowing what I intended to do.
,