Anxiety about fostering kittens

To people who foster kittens while having residents cats in the house….. how do you guys deal with the fear of getting resident cats sick?! I have two kittens quarantining in my bathroom right now that i found in my backyard and I’m still SO nervous about the possibility of them transmitting something to my cats. Maybe I’m overthinking it but I’m afraid I could track something on my shoes when i visit them into the main house and my cats could get in contact with some type of bacteria or virus, even though the kittens were deemed healthy by the vet and my babies are vaccinated. It seems like most vets refuse to do testing for things like panleukopenia on young kittens, which makes sense, but that definitely stresses me out.