The outbreak is romaine lettuce cut up and bagged, then distributed to 23 states is the latest in a series of recent food poisoning cases involving pre-cut and bagged leafy greens.
Twenty-three people in four states have have become sick since March 1, with another seven probable cases, according to the Centers for Disease Control and Prevention.
Out of this a dozen people were hospitalized and three developed a life-threatening type of kidney failure.
The romaine here, was not sold directly to customers in the produce section but was used by food service companies and supermarkets in salad bars and "grab and go" meals. Some of the victims were students at colleges in Michigan, Ohio and New York who apparently ate the infected lettuce in dining halls.
You may remember the 2006 outbreak of E.coli and the Dole bagged spinach that sickened 238 people and caused five deaths.
Most processors of fresh-cut produce remove the outer leaves and core the heads of lettuce in the field, but this is where equipment can come into contact with soil and spread contamination from the dirt to the lettuce.
The E.coli strain associated with human illness often comes from the bacteria spread from the equipment to heads of lettuce. Washing the cored lettuce with a chlorine spray, a standard step, did not kill enough of the bacteria, the researchers found.
Once the bacteria attach to a lettuce leaf, "it's very difficult to remove them," said Robert Gravani, a microbiologist at Cornell University. "We certainly want to increase our consumption of fresh fruits and vegetables, but we really have to address some of these issues."
Caroline Smith DeWaal, food safety director at the Center for Science in the Public Interest, said cross-contamination is another danger. "The process of harvesting lettuce, chopping it or tearing it, washing and putting it in a bag is a process similar to mixing ground beef," she said. "You're taking lettuce that could be grown in different areas and batching it together. So if you've got one infected field, you're mixing it with lettuce that would otherwise be uninfected, and now the whole batch is contaminated."
This current outbreak with the romaine lettuce was contaminated with E.coli strain primarily found in cattle and wildlife feces, and that has never before been linked to a food-borne illness, according to the CDC.
