E. coli O157:H7 is one of the biggest villains in food safety circles, made famous by the 1993 Jack in the Box hamburger outbreak and by later food poisoning cases, including the 2006 spinach outbreak.
But even as bagged-greens companies perfect their new washes, E. coli is turning out to be a moving target, presenting new challenges for safety surveillance.
Scientists are increasingly worried about six lesser-known E. coli strains known as the "big six." One of those strains is blamed for a 2010 outbreak spread by Romaine lettuce that sickened 26 people, largely on the East Coast.
Few companies or health agencies screen for the "big six." Salinas area Earthbound Farm is one that does, and its testing before and after washing has turned up some of those E. coli microbes on some leafy greens — fortunately, before they left the building. The tainted greens were taken to a landfill.