Pre-cut lettuce is suspected cause of food poisoning outbreak
Tuesday, May 18, 2010
It's convenient and popular, a healthy option for harried shoppers. But bagged lettuce suspected of causing a multi-state outbreak of E. coli illness raises new questions about whether pre-cut produce is riskier than whole vegetables.
The outbreak, which involves romaine lettuce cut up and distributed in bags to 23 states and the District, is the latest in a string of recent food poisoning cases involving pre-shredded leafy greens.
Twenty-three people in four states have been sickened since March 1, with another seven probable cases, according to the Centers for Disease Control and Prevention. Of the confirmed cases, a dozen people were hospitalized and three developed a life-threatening type of kidney failure. No deaths have been reported.
The romaine in question was not sold directly to consumers in the produce section but was used by food service companies and supermarkets in salad bars and "grab and go" meals. Several of the victims were students at colleges in Michigan, Ohio and New York who apparently ate the infected lettuce in dining halls.
It is difficult to judge whether pre-cut produce has been linked to more outbreaks than whole vegetables because state and federal health officials don't always specify whether the leafy greens associated with an outbreak were bagged or whole. But several multi-state outbreaks involving pre-cut produce in the last five years have raised concerns, most notably the 2006 outbreak of E. coli O157:H7 associated with Dole bagged spinach that sickened 238 people and caused five deaths.
James Gorny, senior adviser for produce safety at the Food and Drug Administration, said bagged greens represent a disproportionate number of recalls, chiefly because they're easier to identify than whole produce. "When you buy a whole head of lettuce, you have no idea what the brand name is, or who the grower is," Gorny said. "So tracing it back is that much harder."
But, he said, pre-cut produce is not inherently riskier than whole vegetables.
"I've been avoiding bagged lettuce for years," said Michael Doyle, a nationally known microbiologist who directs the Center for Food Safety at the University of Georgia. "I've been concerned about this for some time."
Most processors of fresh-cut produce remove the outer leaves and core the heads of lettuce in the field, where cutting utensils can come into contact with soil and spread contamination from the dirt to the crop, Doyle said. In farming areas, especially in a region near cattle farms, it is not unusual to find E. coli in the soil.
In a study published last year in the Journal of Food Protection, Doyle and several colleagues contaminated coring devices with soil that contained E. coli O157:H7 -- the most common E. coli strain associated with human illness -- and showed how the bacteria spread from the coring 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.
"In a processing plant, you'd have to have walls and clean floors," Doyle said. "But here, they're starting it right out in the dirt. It's a very hazardous practice."
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."
Fresh-cut produce began in the food service industry in the 1980s and then migrated to retail shelves to meet growing consumer demand for a fast, healthful product that required no more preparation than slicing open the bag. According to Nielson Co. ratings, pre-cut salad mix was the top-selling fruit or vegetable between January 2009 and January 2010, outselling heads of lettuce by more than 2 to 1.
"As long as it's treated with respect and handled properly, consumers should feel as confident in the safety of fresh-cut leafy greens as they do in whole-head forms," said Julia Stewart of the Produce Marketing Association.
The current outbreak is drawing special attention because the romaine lettuce was contaminated with E. coli O145, a strain that is primarily found in cattle and wildlife feces and has never before been linked to a food-borne illness, according to the CDC.
Patricia M. Griffin, chief of CDC's Enteric Diseases Epidemiology branch, said it is likely that E. coli O145 has caused previous food poisonings but has gone undetected because only about 5 percent of clinical laboratories are able to detect it. "The fact that we found it now doesn't mean it wasn't there before," she said. "The ability to look for the organism in ill people and in outbreaks and food has been increasing. We're gradually finding more of these organisms."
The FDA, which has repeatedly urged growers to improve produce safety, is crafting what will be the first federal regulations for growing, harvesting and processing fresh produce, Gorny said. The proposed rules are scheduled to be published next year, he said.
In addition, a bill pending in Congress would give the FDA broad new authority to regulate the safety of produce and other foods.
"The FDA needs much more authority to set standards on the farm, and that's contained in the legislation that's been passed by the House and is currently being considered in the Senate, Smith DeWaal said. "The FDA needs to do a much better job at inspecting plants that process and bag lettuce, and it needs to provide better guidance to lettuce producers so they know how to avoid these problems."