i know i'm a bit late to reply to this, but LT, I've had cotton fever from a completely sterile solution as well as filter, needle etc etc. i do admit it wasn't a micron filter but everything was sterile.
though filtering out MOST of the bad stuff, micron filters don't get rid of every little bit of bacteria but the .02 ones will filter out just about every contaminent. so there still is that minute risk of cotton fever.
i'm not disagreeing with you, i highly recommend people use micron filters on every ocassion. unfortunately we don't live in that perfect world where we would have ampoule dispensers an all that jazz so we have to face the possibility of getting cotton fever.