However, scientists believe this parsley was contaminated at the farm in Baja California, Mexico, after harvesting, where it was kept in tap water that had not been chlorinated. At the restaurants, the parsley had been chopped and then not kept refrigerated. Because of North American free trade and a relaxing of global agricultural markets, we are now seeing international outbreaks. Robert Tauxe, the chief of the food-borne and diarrheal diseases branch of the Centers for Disease Control and Prevention in Atlanta, acknowledges that parsley is hardly ever thought to be a source of concern. However, fresh produce of any sort should be rinsed carefully in potable water before use.
Refrigeration is key to keeping bacteria levels low as well.
FSNet, University of Guelph, Ontario, May 11, and 26, 1999.