A Salad Industry Solution to E. Coli Made Things Worse for People and Bees

Researchers find that a recommendation to raze wildlands to stop outbreaks of the pathogen had the opposite effect.

(Photo: Patrick Baur/Courtesy The Nature Conservancy)

Aug 10, 2015· 2 MIN READ
Emily J. Gertz is an associate editor for environment and wildlife at TakePart.

A deadly food poisoning outbreak in 2006 was traced to a spinach field in California’s Central Coast. Because wild pigs in the area were carriers of the E. coli strain, growers came under pressure from the salad greens industry to strip bare the wildlands between their fields.

The idea was that destroying these habitats would reduce the number of wild animals entering the fields and potentially contaminating crops with illness-causing pathogens.

But researchers have found compelling evidence that clearing these lands has made the pathogen problem worse. The study, which analyzed industry data dating to the year after the outbreak, undermines the packaged salad industry’s response to the 2006 E. coli outbreak, when it scrambled to reassure consumers that packaged greens were safe to eat.

A team of scientists from the University of California, Berkeley, found that incidence in leafy greens of pathogenic E. coli—the cause of the 2006 outbreak that made hundreds of people ill and killed three—has increased dramatically, from under 0.1 percent of tested produce in 2007 to 2.5 percent in 2013, according to a study published Monday in Proceedings of the National Academy of Sciences.

The pressure to clear wildlife habitat, however, has led to a 30 percent decrease in the regions remaining meadows and marshes, along with significant amounts of wild grasslands and scrub forest. Those ecosystems are vital for water filtration and retention and support native bees and other pollinators.

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Fresh produce, eaten raw, is now the main cause of food-related illnesses in the United States. But the study’s findings do not translate directly into an increase of contaminated salad greens on supermarket shelves, said lead author Daniel Karp. That’s because packaged salad companies now trace their produce from farm field to point of sale. Contaminated lots are destroyed at the packing facilities before being mixed with other shipments, he said.

To find a relationship between removing vegetation between farm fields and frequency of E. coli and salmonella detection, the researchers gained access to food-testing data for 2007 through 2013 from “a large organic leafy greens corporation,” said Karp, a postdoctoral research fellow at Berkeley in the NatureNet program, which is funded by The Nature Conservancy. “So we could see what was happening to pathogens over time while all this habitat was being removed.”

The researchers also “quantified how much habitat was remaining around over 50 farms in the Central Coast valley growing region and what the prevalence of pathogens was on those farms,” Karp said. “We saw no increase in pathogens on the farms that had the most remaining wild habitat, across all years.”

Karp believes growers should begin restoring wildlife habitat but that their willingness to do it will depend on the salad industry. “Companies like Fresh Express but also packers, shippers, retailers—at all stages of the supply chain where there is risk of loss of consumer confidence—any of those actors can be putting pressure on the growers” to raze wild vegetation, he said.

“Several studies in the same region show that natural habitat is really important for providing pollinators for the farms, and natural enemies to crop pests, including birds and insects,” said coauthor Claire Kremen, a Berkeley ecologist and conservation biologist. “I’d like to see growers become more comfortable again with habitat diversity in the landscape and not worry that it’s going to have a negative effect on their farming.”

She said the Berkeley team would be working with the University of California Cooperative Extension and other regional agricultural organizations to promote the study’s findings among growers.

“There has been this perception that having non-crop habitat near fields was a risk factor,” said Sasha Gennet, a senior scientist with The Nature Conservancy in California. “The science shows this conflict isn’t there.” The group has found that since the 2006 E. coli outbreak, pressure on growers to clear lands has reduced wildlife habitat in the Salinas River Valley 10 to 15 percent overall.

“This region is a global biodiversity hot spot, a place that has Monterey Bay, a very important river,” she said. “So we’re really excited this study is pointing us to a solution.”