How did they become contaminated? Lindemann (the scientist in charge of the investigation) "noted that they are grown with steam in barrels at 100 degrees Fahrenheit, an ideal environment for bacteria to multiply."
The farm in question is "organic", which seems to put it on the side of the angels. But read on: ".......the farmers had not used any manure, which is commonly spread on organic farms and has been known to cause E. coli outbreaks."
It's a bugger when you can't even trust an organic German.