The E. coli Outbreak — Lettuce Learn a Lesson
By Sharon Palmer, RD
Vol. 9 No. 1 P. 28
There are initiatives in place to guard against it—yet contaminated produce led to cases of illness and death. Are food safety regulations too soft or is it a matter of noncompliance?
When the E. coli O157:H7 breakout related to fresh spinach hit the news last fall, it hit big. If people were looking for an excuse not to eat their dark, leafy greens, now they had one. Although people have grown accustomed to being buffeted by food poisoning reports on the evening news, this particular outbreak really hit home.
The sheer scope of the spinach outbreak was undeniable. An estimated 51 cases of illnesses per outbreak are linked with produce.1 This outbreak was roughly four times that size. People wondered for weeks how something as supposedly healthy as fresh spinach could cause illness and death. In a survey by NBC11—which serves San Jose, San Francisco, and Oakland, Calif.—21% of voters to date have indicated that they will never eat spinach again unless it is locally grown.2
The FDA traced the spinach outbreak that sickened 204 people and killed three to four fields on four ranches located in Monterey and San Benito counties in California where the spinach was grown by third-party growers. The FDA reported on September 29, 2006, that all spinach implicated in the outbreak was traced back to the company Natural Selection Foods of San Juan Bautista, Calif.
Not Just a Meat Problem
While our food safety focus has often centered on the processing and handling of raw meat and poultry, this outbreak opened our eyes to a new era of food-borne illness dawning on produce farms. The fact that some consumers open bags of prewashed and prechopped fresh greens and dump them onto their dinner plates without cooking or washing them further increases the gravity of the situation.
For many, the E. coli outbreak in spinach came as no surprise. Since 1998, the FDA has warned fruit and vegetable producers about the potential of E. coli O157:H7 contamination. A previous outbreak in October 2003 involving fresh spinach and E. coli O157:H7 contamination in California resulted in 16 cases of illness and two deaths.
“Fresh produce was not a big source of food-borne illness. It was typically associated with meat items, but now the discussion is on fresh fruits and vegetables. It sounds an alarm for everyone in food safety practices,” says John Krakowski, MA, RD, CDN, a food safety coach in Flanders, N.Y. An approximate 29% reduction in the number of E. coli O157:H7 cases has occurred since 1996 to 1998, thanks to measures targeting ground beef safety and Hazard Analysis and Critical Control Point (HACCP).3
“The general impression among experts in the field is that the number and seriousness of outbreaks is greatest in produce, sprouts, and juices,” says Charles Benbrook, chief scientist at The Organic Center in Enterprise, Ore. The Organic Center recently published a Critical Issue Report on E. coli O157:H7 that discusses its relationship to agriculture.
Under the Microscope
There are more than 225 unique strains of E. coli and the majority of them are not dangerous. E. coli bacteria are essential to the healthy functioning of human and animal digestive systems, but some types have picked up extra genetic material that can turn harmless bacterium into a threat. E. coli O157:H7 is among the most dangerous strains when people are exposed to it. E. coli O157:H7 doesn’t harm cattle because it does not bind to the walls of their gastrointestinal tract. In humans, the bacterium causes diarrhea that is often bloody and can be accompanied by abdominal cramps or fever. Symptoms usually occur within two to three days following exposure. Healthy adults can typically shake E. coli O157:H7, but people at high risk, such as young children and older adults, can develop hemolytic uremic syndrome, which can lead to serious kidney damage and death.
E. coli O157:H7 is particularly pesky because it survives heat, drying, and acidic conditions and causes infections at very low doses. It has also been known to survive in soil for up to six months. The first case of E. coli O157:H7 was reported in 1975 and the first outbreak followed in 1982. The 8,598 cases associated with 350 outbreaks of E. coli O157:H7 reported to the Centers for Disease Control and Prevention from 1982 to 2002 accounted for less than one tenth of 1% of the total number of cases during those years.4
E. Coli’s Link to the Land
As investigators tracked down the source of E. coli O157:H7 contamination in fresh spinach, they discovered that all tests performed on Natural Selection Foods processing facilities by independent scientists and government investigators came up clean, indicating that the E. coli contamination occurred in the fields. The plant’s triple washing procedure didn’t appear to successfully remove the E. coli O157:H7 from the spinach, prompting food safety experts to realize that produce needs to be clean at the time it enters processing.
Specific samples of cattle feces on one of the implicated ranches tested positive based on the genetic fingerprints for the same strain of E. coli O157:H7 responsible for the outbreak. These results brought the whole connection of agriculture and food safety from the shadows. Since E. coli can survive in soil, water in troughs, and raw cattle manure for months, consider the myriad ways it could find itself onto a wrinkly leaf of spinach. The outbreak highlights how farming systems, cattle and dairy cow manure, animal husbandry and feeding practices, irrigation water quality, sanitation in field workers, fertilizers, and agricultural regulations play into food safety.
Perhaps it was a red flag when cases of E. coli O157:H7 illness were reported due to children being infected at county fair petting zoos. Approximately 11% of the cattle fecal samples tested for E. coli O157:H7 at Minnesota county fairs in 2000 and 2001 tested positive.5
The Farm, an Open Environment
Farms are all about wide open spaces—you can’t seal them off into sterile biospheres. Issues of previous land use, adjacent land use practices, and water safety all come into play. And then there’s that nagging problem of animal waste from nearby livestock or even wildlife.
Krakowski points out, “Fruits and vegetables are grown in nature’s restroom.” Agricultural experts believe that even wildlife and birds may play a role in spreading E. coli. Indeed, investigators found a positive match for E. coli O157:H7 in the guts of a feral pig killed on the property of one of the identified ranches where the strain was found. There were signs that pigs had broken through a fence to eat the spinach.
Although officials have not pinpointed feral pigs as the bacteria’s carrier, this discovery has caused concerns about access of wildlife to crops.
Enough Bugs to Go Around
Just ponder the many ways E. coli could rear its ugly head on a farm and plenty of ideas pop into your head. “My first thought when I heard about the spinach outbreak was: Did a farmer change his [child’s] diaper … before heading to the fields without first washing his hands?” says Amy Barr, MS, EdM, RD, cofounder of Marr Barr Communications, a strategic marketing and communications agency specializing in food, nutrition, health, lifestyle, and sustainability. Officials reported that the contamination route for the spinach outbreak may have been via wandering livestock, substandard worker hygiene, irrigation practices, or even wild boar.
One farming issue experts worry about is manure practices. Benbrook reports that there are clearly problems that arise as a result of manure lagoons and manure overflowing. Dairy farms using concrete alleys and flushing systems were eight times more likely to test positive for E. coli O157:H7 than other manure removal systems. Benbrook suggests improvements can come from developing vegetative buffer strips along creeks and irrigation canals and having healthy, biologically active, organic soil with many different microbes that decrease pathogens due to competition.
A study looking at E. coli O157:H7 cases in Canada found that the application to cropland of raw manure by a manure spreader or as liquid slurry was the second most significant variable explaining the geographic distribution of E. coli illnesses. (The strongest association was for the ratio of cattle to humans.)6
“We always need to control any run-off problems. Run-off can cause huge cross-contamination issues around both big and small farms,” says Barr, who grew up on a small farm in the Midwest and recently observed a farmer in New England using a front-end loader to dump manure from a barn onto his land with a stream running through it.
The manure problem flows right into another big area of concern: water. The potential for irrigation ditches and canals to be contaminated is a serious risk. We know contaminated drinking water and water in lakes and pools have triggered cases of illness linked to E. coli O157:H7 in the past.
“A big eye opener is water and how we use water and take care of water. When we pollute water in one part of the food system, it comes back to bite us in another part—it is all connected,” says Alison H. Harmon, PhD, RD, LN, assistant professor of food and nutrition and director of the dietetics program at Montana State University and Sustainable Agriculture and Food Systems cochair of the Hunger and Environmental Nutrition Dietetic Practice Group.
The Great Cattle Debate
When samples of cattle fecal matter from one implicated ranch from the spinach outbreak tested positive for the same strain of E. coli bacteria that sickened people, the link between cattle and crops became significant. The fecal matter specimens were found one half mile to one mile from the produce field, which abutted the livestock pastures.
Most of E. coli O157:H7 comes from the digestive systems of beef and dairy cattle. Less than 1% to more than 10% of cattle tested are found to shed E. coli O157:H7, which enters the environment when it is shed in the manure of infected cattle. Once unleashed in the environment, other animals can harbor it without apparently suffering from it.
“It is clear that cattle on forage diets are much less likely to shed E. coli O157:H7 in manure than grain-fed cattle,” says Benbrook. When cows are fed high-energy, grain-based diets, the pH in their digestive systems changes to favor E. coli O157:H7. But Barr notes that while there’s a lot to be said for avoiding feeding excessive amounts of grains to ruminants, after frost and before spring greening ranchers in most areas of the country can’t rely on pasture. “Snow happens. Plus, most ‘pasture-based’ farmers, especially dairy farmers, also supplement their livestock’s diets with grain,” says Barr. “It’s not black and white. If you feed cattle less grain, you’re not going to eliminate E. coli.”
Some also argue that antibiotic use on livestock fosters genetic mutations capable of turning generic E. coli into a dangerous variant such as E. coli O157:H7. “It is widely accepted that the antibiotics used in livestock accelerate the rate of genetic adaptation in bacteria. The evidence is overwhelming that antibiotics in pork and poultry lead to the emergence of new antibiotic-resistant strains of bacteria,” says Benbrook. “If there’s one antibiotic-resistant gene somewhere in the environment, there are numerous ways to get it into cattle. Agriculture has done far more than its fair share to create antibiotic-resistant bacteria and further spread it.”
Research has found varying levels of antibiotic resistance in E. coli O157:H7 serotypes. A study on isolates from cattle, humans, swine, and farms collected from 1985 to 2000 found that 39% of the E. coli isolates were resistant to one or more antimicrobials.7
One Big Salad Bowl
Here’s a good question: Do people even think about where the leafy greens came from before they rip into a pretty, cellophane bag of precut salad purchased at their local supermarket? It was a shock when the spinach outbreak highlighted the fact that the spinach involved in making people sick in 26 different states and Canada all came from Natural Selection Foods in the Salinas Valley. To make matters worse, five other companies issued voluntary recalls since their products may have contained spinach from Natural Selection Foods. On top of that, Natural Selection Foods has 20 other brands—from Earthbound Farm and Dole Food Company, Inc. to Trader Joe’s and Sysco—that were also recalled. Salinas Valley isn’t called the “nation’s salad bowl” for nothing—75% of the country’s fresh spinach comes from this region.
Jennifer Wilkins, PhD, RD, senior extension associate at the division of nutritional sciences at Cornell University, pointed out in her “Food Citizen” column in the Albany Times Union on October 1, 2006, that the outbreak was amplified because the contaminated spinach from one or a few farms was mixed with spinach from numerous other farms, then bagged by a few processors, marketed under several brands, and distributed nationally and internationally.8 This sort of centralized food system has more opportunities for contamination that can reach many people, while a smaller, local food system is easier to trace and does not offer such widespread consequences.
“One big problem is the traceability of foods. When people buy their food in a grocery store, they don’t know how it got there. We do not know the history of the food and we have lost our connection to the land,” says Harmon. “I see this as an encouragement to localize.”
Regulations Down on the Farm
Experts feared the big one was coming. There had been 19 outbreaks of food-borne illness caused by E. coli O157:H7 in lettuce or leafy greens. The FDA had written a letter to the lettuce industry in November 2005 warning about the ongoing risk for product contamination. The FDA developed the Lettuce Safety Initiative in response to recurring outbreaks of E. coli O157:H7 in lettuce with the goal of reducing public health risk by focusing on the product, agents, and areas of greatest concern. In August 2006, the California Department of Health Services, the USDA, and the FDA met with industry and academia to further clarify the goals and plan the Lettuce Safety Initiative. Then all hell broke loose.
What sort of regulations are in place for produce growers? Farmers need to comply with FDA, Environmental Protection Agency, USDA, Occupational Safety & Health Administration, U.S. Department of Labor, and state and local regulations. The FDA also developed the voluntary Guide to Minimize Microbial Food Safety Hazards for Fresh Fruits and Vegetables in 1998, which offers the industry guidance on Good Agricultural Practices (GAPs). The guide covers agricultural water, wild and domestic animals, worker health and hygiene, the production environment, postharvest water quality, and sanitation of faculties and equipment.
“The current food safety program components or tools such as GAP, HACCP, and GMPs [Good Manufacturing Practices] are sound and effective at reducing risk of food-borne illness. But clearly everyone in the industry must know about these tools and understand how to use them effectively,” says David Gombas, PhD, vice president of scientific and technical affairs at United Fresh Produce Association.
In reaction to the spinach outbreak, the FDA and the State of California now expect the industry to develop a plan that will minimize the risk of another outbreak, but the implementation of the plan will be voluntary. One big problem some complain about is the word voluntary, which shows up in guidelines to the industry.
Marion Nestle, PhD, MPH, reported in an editorial posted on October 23, 2006, in The Mercury News that the food safety system needs an overhaul, noting that Congress has not given the FDA the authority or resources to enforce safety procedures on farms.9
Building Farm Firewalls for Food Safety
Some produce growers and processors are taking charge of food safety. “The industry is evaluating and enhancing best practices, evaluating and recommending means of compliance, and, together with the government, academia, and industry experts, developing a long-term research agenda. We now must focus on ensuring industrywide compliance of current and future best practices,” says Gombas.
Natural Selection Foods and Earthbound Farm set in place an unprecedented food safety program on September 28, 2006, that includes rigorous testing and analysis of field operations from the seed to harvest. They report that the seed, irrigation water, soil, soil amendments, plant tissues, and wildlife will be tested, monitored, and certified. The sanitation protocols for farm equipment, packaging supplies, and transportation vehicles will be enhanced and monitored. And they have installed a “firewall,” which means that every lot of freshly harvested greens brought to their facility will be tested before entering their processing stream. This program is modeled after the program the beef industry successfully implemented.
Earthbound Farm reported that they will have heightened protocols fully implemented in all growing fields by spring 2007, such as certifying that seeds are free of pathogens prior to planting; certifying that soil amendments such as compost and fertilizers are free of contaminants before they are used; testing and monitoring water sources for harmful bacteria; regularly monitoring environmental conditions in the field; making frequent, unannounced inspections of growers’ fields and equipment; training field harvesters on quality standards and sanitation; and refrigerating salad greens within the hour they’re harvested and maintaining an unbroken cold chain.
Benbrook says, “I take my hat off to Natural Selection Foods. These are unprecedented preventative food safety measures.”
Western Growers, an agriculture trade association whose members grow, pack, and ship 90% of the fresh fruits, nuts, and vegetables grown in California and 75% in Arizona (roughly one half of the nation’s fresh produce), also announced that it would take action to initiate a California Marketing Agreement and a Marketing Order that would establish mandatory GAPs to strengthen spinach and leafy green food safety practices.
Education on the Farm-Food Safety Connection
The FDA and growers have pointed out that consumers need to be educated that fresh perishable produce and precut or peeled produce need to be stored in a clean refrigerator at temperatures of 40° F or below. The FDA, in conjunction with the Produce Marketing Association and the Partnership for Food Safety Education, has developed a national produce handling education campaign to help better educate consumers on handling produce.
“Dietitians need to know about food safety. We have to be spokespeople. We want people to have faith in the food supply,” says Krakowski, who reports that something as simple as educating people to rinse fruits and vegetables and use vegetable brushes on produce before they are consumed is important. “Food safety is part of the dietary guidelines. It should be included when dietitians talk to their clients.”
“I think some dietitians have a hard time seeing how agriculture relates, but it’s all related to health,” says Harmon, who notes that educating the public about food safety is an important part of the field. “The first message is to keep food safe in the kitchen, and then there’s keeping it safe in the big picture, which involves a discussion about knowing how food is grown and how it is produced. We have a big job to do.”
— Sharon Palmer, RD, is a contributing editor at Today’s Dietitian and a freelance food and nutrition writer in southern California.
1. Smith DeWaal C, Barlow K, Hicks G. Outbreak Alert! Closing the Gaps in Our Federal Food-Safety Net. 2005. Washington, D.C. Center for Science in the Public Interest. Available at: http://www.cspinet.org/new/pdf/outbreakalert2005.pdf
2. NBC11 Exclusive: Preventing Spinach E. coli Outbreak, Survey: Will you Eat Spinach Again? Available at: http://www.nbc11.com/news/10234732/detail.html
3. FoodNet. Preliminary FoodNet Data on the Incidence of Infection with Pathogens Transmitted Commonly Through Food — 10 States, United States, 2005. MMWR. 2006;55(14):392-395.
4. Rangel JM, Sparling PH, Crowe C, et al. Epidemiology of Escherichia coli o157:H7 outbreaks, United States, 1982-2002. Emerg Infect Dis. 2005;11(4):603-609.
5. Cho S, Bender JB, Diez-Gonzalez F, et al. Prevalence of shiga toxin-encoding bacteria and shiga toxin-producing Escherichia coli isolates from dairy farms and county fairs. Vet Microbiol. 2006;118(3-4):289-298.
6. Valcour JE, Michel P, McEwen S, et al. Associations between indicators of livestock farming intensity and incidence of human Shiga toxin-producing Escherichia coli infection. Emerg Infect Dis. 2002;8(3):252-257.
7. Schroeder CM, Zhao C, DebRoy C, et al. Antimicrobial resistance of Escherichia coli o157 isolated from humans, cattle, swine, and food. Appl Environ Microbiol. 2002;68(2):576-581.
8. Wilkins J. Food safety should be a priority. Albany Times Union. October 1, 2006. Available here.
9. Nestle M. The Spinach fallout: Restoring trust in California produce. The Mercury News. October 23, 2006. Available here.
Safe Produce Resource Guide
Centers for Disease Control and Prevention, http://www.cdc.gov
FDA, Center for Food Safety and Applied Nutrition, http://www.cfsan.fda.gov
Gateway to Government Food Safety Information, http://www.foodsafety.gov
International Food Information Council, http://www.ific.org
National Restaurant Association Educational Foundation, http://www.nraef.org
Partnership for Food Safety Education, http://www.fightbac.org
USDA Food Safety Information Center, http://foodsafety.nal.usda.gov
Onions, Lettuce, E. coli … Oh My!
Hold the onions, er, lettuce, please? In the most recent food contamination incident to date, as many as 71 people in the Northeast were sickened with E. coli bacteria late last November with a link to Taco Bell. Taco Bell leaned toward green onions (which are sprinkled on many of their food items) as the contaminated food source, but after investigation, the Centers for Disease Control and Prevention named lettuce as the likely source, although cheddar cheese and ground beef were also considered.
Five states, primarily New Jersey, New York, and Pennsylvania, were affected by the outbreak, as health officials and restaurant owners struggled to find the culprit food source to maintain food safety for customers. More than 90 of Taco Bell’s 5,800 nationwide restaurants closed for several days during the scare, and all stopped using green onions altogether—the first suspected E. coli source. As an extra precautionary measure, Taco Bell, owned by Yum! Brands, Inc., changed its Northeastern produce supplier.
In an unrelated incident late last November, approximately 50 people sustained symptoms related to E. coli poisoning and several were hospitalized after eating at another taco chain, Taco John’s, in the Midwest.
— Juliann Payonk is an editorial assistant at Today’s Dietitian.