fennho... i can understand your concern, but just to let you know...we board dogs for a living. we often have over 12 dogs at a time. it would have been impossible to keep the dogs and the children separated. neither of my children have become sick from the dogs, in any way.
i find that many, including doctors and nurses, in hk have no clue what having a dog is actually like. i had nurses and doctors both ask me what i was going to do with my dogs once the first baby arrived.
if your dog is always out for a walk and you are concerned, then clean its feet when it comes home. it only takes a minute and you'll feel 'safer'.