It's never been a problem for me (I have had bunnies with Pasteurella & EC) but I am very careful with hygiene to avoid cross contamination (wear disposable gloves, each hutch has own accesories and cleaning equiptment, regularly disinfect and so on).
Personally I have never found Snuffles as contagious as people previously led me to believe. There was also research sometime ago (2-3 years I think) that suggested some rabbits were born predisposed to developing snuffles and it often laid dormant until an immune crisis.
It's also worth remembering it works both ways, your bunnies *could* be exposed to something carried by a foster.
