Three recent outbreaks of food-borne illnesses traced to bagged spinach or lettuce from California have led some scientists and food safety advocates to suggest that packaging greens might contribute to the spread of a lethal strain of E. coli bacteria.
In particular, the centralized processing of fresh greens can increase the risk of more widespread contamination, just as tainted beef from one steer can find its way into hundreds of packages of ground meat, said Dr. David W.K. Acheson, chief medical officer at the U.S. Food and Drug Administration's Center for Food Safety and Applied Nutrition.
"If you have a single head of [tainted] lettuce that winds up in someone's home, makes the family sick, chances are it'll never get on the radar screen," Acheson said. "If you take the same lettuce, process it ... one head may contaminate multiple bags. Then you've got an outbreak."
The way some greens are harvested also has raised concerns, said Michael Doyle, director of the University of Georgia's Center for Food Safety, who was recently hired by Taco Bell to review its safety guidelines.
For The Record
Los Angeles Times Thursday January 25, 2007 Home Edition Main News Part A Page 2 National Desk 2 inches; 71 words Type of Material: Correction
Bagged lettuce: An article in Saturday's Section A reported that some scientists and food safety advocates believe that packaging greens might contribute to the spread of a lethal strain of \o7E. coli bacteria and included a photograph of bagged lettuce in a grocery store. The photo showed rows of Fresh Express products; however, that company has not been identified as being associated with any of the recent outbreaks of food-borne illnesses.
"I quit eating bagged lettuce years ago," Doyle said. "After seeing how bagged lettuce was harvested and prepared, my impression was it's not very sanitary."
Doyle referred specifically to bagged iceberg lettuce, which has been investigated in the simultaneous but separate Taco John's and Taco Bell outbreaks of Escherichia coli O157:H7 that sickened more than 150 customers in the Midwest and on the East Coast in November and December.
Officials have linked those outbreaks to farms in the Central Valley and possibly on the coast south of Salinas.
The illnesses occurred only months after another leafy green, spinach, was blamed in an outbreak that killed three people and sickened more than 200 in late August and early September. That outbreak was traced to bagged spinach from the Greater Salinas Valley, which was sold in stores nationwide.
The upshot is that pre-washed and packaged produce, a $3-billion industry created to improve both safety and convenience, is under a cloud. Though the individual consumer's risk of illness remains small, experts said, the only practical way to ensure that greens are free of E. coli is to thoroughly cook them -- not a desirable option for lettuce.
E. coli is commonly found in healthy cattle and shed through their feces. Federal and state officials believe that produce outbreaks occur when bacteria-carrying manure gets into fields via livestock, water, birds or other wildlife.
Iceberg lettuce intended for packaging is vulnerable to contamination in part because it is often cut and initially processed in the field, Doyle said. The core is cut out of the head and discarded, as are the protective outer leaves.
"When you've chopped that product, you've created a lot more avenues for bacteria to enter, especially if you're doing it in the fields," said Bob Martin, general manager of Rio Farms in King City. Once the bacterium "is locked into that cut edge of lettuce, then it's really difficult for your chlorine bath to kill it."
Processing plants wash leafy greens three times in chlorinated water before bagging them. They also employ other safety measures, including guidelines for field-cored lettuce, said Jim Gorny, senior vice president for food safety and technology at United Fresh Produce Assn., a trade group.
He said the harvested heads are put on a conveyor belt, sprayed with cooled, chlorinated water, placed in a bin with a plastic liner and shipped to the processing plant.
By discarding the core and outer leaves in the field, Gorny said, "you're actually bringing in a microbiologically cleaner product into your sterilized plant."
Spinach is harvested by machines like lawn mowers. Contamination in the field is possible but less likely than with iceberg lettuce, Doyle said.
But both lettuce and spinach destined for packaging generally are trucked to centralized processing plants, where tainted and untainted leaves can be mixed during chopping, washing and bagging. By contrast, greens that are not bagged are not chopped up and mingled.
Although washing in chlorinated water should kill E. coli bacteria, it takes only a small amount to make someone sick -- about 10 organisms, or 2% of the space on the head of a pin.
The bagged greens industry has consolidated so much that a single contamination problem can threaten the entire industry, said Timothy York, chief executive officer of Markon Cooperative Inc., a Salinas-based produce purchaser for food service distributors. According to the Produce Marketing Assn., nearly 90% of the retail market for packaged salads is controlled by only two companies: Dole Fresh Vegetables and Fresh Express.