Interesting! It's never once occurred to me that I might be kissing my gentleman’s wife, GF or the last SW he saw when he kisses me. Nor do I think about that when I press lips with another SW. It makes for some hilarious spin-offs though, like if you shake hands with another guy, do you have his dick on your hand now? Imagine at a conference, that’s 15 dicks easy.
In all seriousness, if you’re preoccupied with thoughts of cooties, seeing a sex worker is not the best choice for you. Maybe pick someone who isn’t sexually active so you can know you’re the only one.
As for real germs, Listerine is a libertine’s best friend.