I also believe besides years and years ago with one issue (which they have since made it more "clean").. that there is a VERY low risk of any contaminant!!
My symptoms all started after a blood transfusion for a botched simple procedure (and I was post partum too).. I was seronegative for CMV a few weeks before birth of my son, and a few weeks after - after the blood transfusion - I was CMV positive... I am ALWAYS curious if this is related, but no one seems to even want to investigate it??! They won't even check on my blood donors to see if they are still alive or suffering from any illness... all they can tell us iis- they were fine when they donated... UGh!! Well of course, or else hopefully they wouldn't have been allowed to!