Header graphic for print

Food Safety News

Breaking news for everyone's consumption

Researchers Try to Explain E. coli in Produce

A new field study by UC Davis scientists has measured the incidence of E. coli O157:H7 in the feces of Northern California wildlife. This study, funded by the U.S. Department of Agriculture (USDA) and the U.S. Food and Drug Administration (FDA) found E. coli O157:H7 in some wildlife stool samples. However, these samples may not be enough to explain the numerous E. coli O157:H7 outbreaks in leafy greens over the past decade.

This study was designed in response to the massive spinach E. coli O157:H7 outbreak of 2006 in which over 200 people were sickened across the country and three people died.

lettuce-field4-featured.jpgTim York, Chairman of the Board of Advisors of the Center for Produce Safety opened the Produce Research Symposium in May by emphasizing the impact the 2006 outbreak had on the produce industry.  Jim Prevor reported York’s opening remarks on his blog: “Those of us in agriculture and particularly those in the Salinas Valley will never forget where we were that night either… for as Kennedy’s death changed the course of history, San Benito spinach and September 14, 2006, changed the course of history for the produce industry.”

This outbreak prompted a number of studies designed to figure out how lethal strains of E. coli contaminate leafy produce.

In 2008 the UC Davis study team began testing stool samples for most mammals native to the northern California farming region. The research team collected over 1,100 samples from animals such as feral pigs, mice, crows, coyotes and cowbirds.

Robert Mandrell, a principal investigator in the studies and research leader with the USDA Center for Produce Safety and Microbiology Research, concluded, “The fact that we have identified two bird species with an incidence of E. coli O157:H7 of more than 3 percent, feral swine with about a 4 percent incidence, and several coyotes and rodents that tested positive for E. coli O157:H7 suggests there are at least several sources of pathogen movement in this region.”

Researchers say it is difficult to determine if wildlife is the direct source of contamination for Salinas Valley produce. They think that environmental factors such as draught, heavy rainfall, and wind are also playing a part. Additional studies are being conducted on the reptiles and amphibians of the region, as well as weather and watersheds.

Mandrell explained that his team has collected over 11,000 samples so far from wildlife, water, and soil.  Team members are currently trying to connect the dots between these samples and the many natural environmental factors native to the “salad bowl” region.

They believe that wind, rainfall, precipitation, and distance from watersheds to crops all play into the movement of dangerous E. coli strains, and are working to find patterns throughout the enormous data sets they have collected through their multi-million dollar study.

At this point, no single area of study has produced a conclusive set of answers.  In Mandrell’s words, “We are looking at the ranches and watersheds and wildlife around these regions, getting an idea about how things are moving through this environment. We are analyzing E. coli in water, wildlife, and livestock and using microbial source tracking to connect the strains.”

What do their findings so far tell us about E. coli O157:H7 outbreaks?  Mandrell responded, “It appears that big outbreaks result from a convergence of unusual and random events. Now we don’t always know what all those are, but if we think back to the spinach outbreak of 2006, certainly there were some record high temperatures during planting and prior to harvesting. There certainly was wildlife intrusion. There was a convergence of multiple things that shouldn’t happen.”

He continued, “Everybody is starting to realize that maybe unusually heavy rainfall prior to planting could be an issue in terms of where water is routed.”

Some of these factors can be controlled in an effort to reduce contamination. For instance, many farmers are blocking wildlife from their crops. “The industry is certainly aware of most of the problems, certainly keeping wildlife such as pigs, deer, and small rodents out.”

However, some things are harder for farmers to manage. “Birds are extremely difficult to control,” Mandrell explained.

When asked about what else the industry can do to avoid contamination Mandrell said, “I think there is a certain randomness to this, but I would say certainly when we have abnormally high rainfall maybe the industry needs to be extra vigilant.”

Mandrell believes that E. coli O157:H7 may be naturally embedded into the California environment. This claim begs the question, does he think E. coli O157:H7 outbreaks in leafy produce can be avoided?  When Food Safety News asked Mandrell he replied, “I think that’s a loaded question.  At this point you can definitely minimize the risk of outbreak. People are going to have to come together and brainstorm. We are trying to provide information that can be useful and give some direction for the industry.”

At this point, it seems like it may be extremely difficult to completely eliminate any chance of contamination in produce.  Mandrell says, “Zero tolerance for an industry that is outdoors is very difficult. Everyone wants to try and have sterilized produce grown and this will be extremely hard. But the farmers, they are trying.”

His studies involved the cooperation of many different farms. Over 38 private properties were involved with one study, but Mandrel stressed the importance of confidentiality.

When asked if he felt the industry was cooperating with the team’s research Mandrell said he felt the industry has tried.  “They feel put upon; the ones who are cooperating, I really give them credit. Some don’t want to cooperate because it is so sensitive for them, but overall, I have been very pleased with the industry’s cooperation.”

The intensive sampling study Mandrell has been working on will finish up around early October of this year, but scientists will continue animal stool sampling on a much smaller scale with a possible focus on birds or geese.

Mandrell thinks that conclusions in the form of formal reports and papers will be released over the next couple of years. “We put so much effort and money into this but it is still just a snapshot,” he said. Scientists agree that long-term studies on weather patterns may unearth more answers.

If there is a chance that E. coli O157:H7 may be embedded in parts of the northern California’s agricultural environment, Mandrell’s team hopes their studies will provide the industry with direction towards radically reducing and eventually eliminating the environment’s risk to consumers.

© Food Safety News
  • Errol Hess

    Doesn’t this beg the question of whether the e coli source is in the processing and conditions transporting produce thousands of miles?

  • Ann Quinn, consumer

    As a consumer,now I’m confused and would like to ask for expert opinions. Mr. Hess’ question seems like an important
    one on transport of produce and E. coli exposure.
    And I thought beef cows were a principal shedder of E. coli 0157:H7 in feces, especially if fed other than a grass diet. Yet in this article there is no mention of large scale industrial farm production by dairy cows or cows raised for slaughter in large feed lots.
    Is there no relationship between cow factory farms and possible
    runoff from waste products via water into any produce fields in the proximity?

  • http://wellnessforallnow.blogspot.com/ Janice Epstein

    I’m with Errol. I am also surprised not to hear at least a little something about testing the fertilizer the farms are using.