Probably the same cause as the Spinach with Salmonella. That was caused, it is speculated because of the research which showed the farms where some of it came from, by the cows that were on the other side of the fence. That would mean that cow shit caused the salmonella, and I would assume that this is the same cause for the tomatoes. That would be the cow shit from the other side of the fence. Organic after all is organic.
Suggestion - wash your food from the fields before you eat it, and better yet cook it first.