Re the necessity of washing mushrooms. The stuff they are grown in commercially sounds foul, and in fact is, but it is sterilized prior to inoculation with mushrooms.
If there is any infection risk it would be from the human hands that touch each one at harvest and the hands that pack them.
Assuming, of course, that there isn't willful contamination with a little spit etc. because of a labor dispute or just a bad attitude. Living where I do in the heart of mushroom country, one hears stories....
FWIW I won't eat them raw.