Romaine lettuce has a long history of E. coli outbreaks, but scientists are zeroing in on why. A new study reveals that the way lettuce is irrigated—and how it’s kept cool afterward—can make all the difference. Spraying leaves with untreated surface water is a major risk factor, while switching to drip or furrow irrigation cuts contamination dramatically. Add in better cold storage from harvest to delivery, and the odds of an outbreak plummet. The research offers a clear, science-backed path to safer salads—one that combines smarter farming with better logistics.
FULL STORY
Scientists have traced major E. coli risks in romaine to how it’s watered and cooled. Changing irrigation methods and improving cold storage could dramatically reduce contamination. Credit: Shutterstock
E. coli outbreaks in romaine lettuce have long been a public health concern. and now a new Cornell University paper suggests that a combination of efforts in the field, and even postharvest techniques, can minimize risk to human health.
Co-authored by Renata Ivanek, a professor in the department of population medicine and diagnostic sciences, and Martin Wiedmann, professor in food safety, the paper outlines interventions likely to make a concrete difference in the safety of the nation's romaine.
"This study supports that interventions should focus on reducing produce contamination via contaminated irrigation water, on assuring that produce washes applied during processing consistently deliver reasonably high reductions of bacterial numbers, and on improving temperature control during distribution," Wiedmann said.
"We tried to describe the system as holistically as possible to account for different risk factors and how they could have interactions," Ivanek said. "There's not just one intervention that will save us all. We spent a lot of time trying to understand the preharvest component, especially the irrigation water piece and how much risk can be explained by that."
Study results suggested that much contamination originates from irrigation with untreated surface water applied through overhead spray irrigation systems. They found that risk from irrigation was reduced either through water treatments or by switching to furrow or drip irrigation.
"While not the most common system, spray irrigation is used in a number of fields for its benefits during germination, its cooling effect on plants and other reasons. But drip or furrow irrigation reduces the probability that water directly touches the leaves," Ivanek said, acknowledging that switching to these other irrigation systems introduces significant potential additional costs to grower.
Ivanek and her co-authors also explored the importance of maintaining proper cold storage temperatures along the entire supply chain to romaine's final destination.
"Time and temperature play a role in food safety, and also in food quality and shelf life," she said, describing a "perfect storm" if contamination happens at the farm or processing level and then improper transportation temperatures allow bacteria to grow.
The comprehensive practices and interventions explored in this study intend to aid decision-makers in establishing and enhancing food safety best management practices, Ivanek said.
"The big message is the American food supply chain is extremely safe compared to other countries," she said. "We're exploring how can we make it even safer and where we should put additional effort."
Story Source:
Materials provided by Cornell University. Note: Content may be edited for style and length.
Journal Reference:
Ece Bulut, Sarah I. Murphy, Laura K. Strawn, Michelle D. Danyluk, Martin Wiedmann, Renata Ivanek. Risk assessment of Escherichia coli O157:H7 along the farm-to-fork fresh-cut romaine lettuce supply chain. Scientific Reports, 2025; 15 (1) DOI: 10.1038/s41598-025-01585-z[1]
Cite This Page:
Cornell University. "Dirty water, warm trucks, and the real reason romaine keeps making us sick." ScienceDaily. ScienceDaily, 19 July 2025. <www.sciencedaily.com/releases/2025/07/250718031225.htm>.
Cornell University. (2025, July 19). Dirty water, warm trucks, and the real reason romaine keeps making us sick. ScienceDaily. Retrieved July 19, 2025 from www.sciencedaily.com/releases/2025/07/250718031225.htm
Cornell University. "Dirty water, warm trucks, and the real reason romaine keeps making us sick." ScienceDaily. www.sciencedaily.com/releases/2025/07/250718031225.htm (accessed July 19, 2025).
May 5, 2025 Vertical farming can do more than lettuce. A research team has investigated the cultivation of six food groups in vertical farming: Crops, algae, mushrooms, insects, fish and cultivated meat. In this ...
Feb. 29, 2024 Leafy green vegetables are important sources of dietary fiber and nutrients, but they can harbor harmful pathogens. In particular, lettuce has often been involved in outbreaks of foodborne illness ...
Aug. 14, 2023 With climate change, irrigating more crops in the United States will be critical to sustaining future yields, as drought conditions are likely to increase due to warmer temperatures and shifting ...
Mar. 17, 2022 Marine cold spells are cold versions of heat waves: periods of exceptionally cold water, able to hurt or help the ecosystems they hit. Today, the oceans experience just 25% of the number of cold ...
Jan. 28, 2022 In the U.S., 52% of irrigated land is used for corn, soybean and winter wheat production. Corn and soybean are two of the country's most important crops, with 17% of corn production and 12% of ...
July 5, 2021 Bioenergy with Carbon Capture and Storage (BECCS), a negative emission technology, has been considered inevitable to achieve the 2°C or 1.5°C climate goal. Although numerous studies have been ...
Romaine lettuce has a long history of E. coli outbreaks, but scientists are zeroing in on why. A new study reveals that the way lettuce is irrigated—and how it’s kept cool afterward—can make all the difference. Spraying leaves with untreated surface water is a major risk factor, while switching to drip or furrow irrigation cuts contamination dramatically. Add in better cold storage from harvest to delivery, and the odds of an outbreak plummet. The research offers a clear, science-backed path to safer salads—one that combines smarter farming with better logistics.
FULL STORY
Scientists have traced major E. coli risks in romaine to how it’s watered and cooled. Changing irrigation methods and improving cold storage could dramatically reduce contamination. Credit: Shutterstock
E. coli outbreaks in romaine lettuce have long been a public health concern. and now a new Cornell University paper suggests that a combination of efforts in the field, and even postharvest techniques, can minimize risk to human health.
Co-authored by Renata Ivanek, a professor in the department of population medicine and diagnostic sciences, and Martin Wiedmann, professor in food safety, the paper outlines interventions likely to make a concrete difference in the safety of the nation's romaine.
"This study supports that interventions should focus on reducing produce contamination via contaminated irrigation water, on assuring that produce washes applied during processing consistently deliver reasonably high reductions of bacterial numbers, and on improving temperature control during distribution," Wiedmann said.
"We tried to describe the system as holistically as possible to account for different risk factors and how they could have interactions," Ivanek said. "There's not just one intervention that will save us all. We spent a lot of time trying to understand the preharvest component, especially the irrigation water piece and how much risk can be explained by that."
Study results suggested that much contamination originates from irrigation with untreated surface water applied through overhead spray irrigation systems. They found that risk from irrigation was reduced either through water treatments or by switching to furrow or drip irrigation.
"While not the most common system, spray irrigation is used in a number of fields for its benefits during germination, its cooling effect on plants and other reasons. But drip or furrow irrigation reduces the probability that water directly touches the leaves," Ivanek said, acknowledging that switching to these other irrigation systems introduces significant potential additional costs to grower.
Ivanek and her co-authors also explored the importance of maintaining proper cold storage temperatures along the entire supply chain to romaine's final destination.
"Time and temperature play a role in food safety, and also in food quality and shelf life," she said, describing a "perfect storm" if contamination happens at the farm or processing level and then improper transportation temperatures allow bacteria to grow.
The comprehensive practices and interventions explored in this study intend to aid decision-makers in establishing and enhancing food safety best management practices, Ivanek said.
"The big message is the American food supply chain is extremely safe compared to other countries," she said. "We're exploring how can we make it even safer and where we should put additional effort."
Story Source:
Materials provided by Cornell University. Note: Content may be edited for style and length.
Journal Reference:
Ece Bulut, Sarah I. Murphy, Laura K. Strawn, Michelle D. Danyluk, Martin Wiedmann, Renata Ivanek. Risk assessment of Escherichia coli O157:H7 along the farm-to-fork fresh-cut romaine lettuce supply chain. Scientific Reports, 2025; 15 (1) DOI: 10.1038/s41598-025-01585-z[1]
Cite This Page:
Cornell University. "Dirty water, warm trucks, and the real reason romaine keeps making us sick." ScienceDaily. ScienceDaily, 19 July 2025. <www.sciencedaily.com/releases/2025/07/250718031225.htm>.
Cornell University. (2025, July 19). Dirty water, warm trucks, and the real reason romaine keeps making us sick. ScienceDaily. Retrieved July 19, 2025 from www.sciencedaily.com/releases/2025/07/250718031225.htm
Cornell University. "Dirty water, warm trucks, and the real reason romaine keeps making us sick." ScienceDaily. www.sciencedaily.com/releases/2025/07/250718031225.htm (accessed July 19, 2025).
May 5, 2025 Vertical farming can do more than lettuce. A research team has investigated the cultivation of six food groups in vertical farming: Crops, algae, mushrooms, insects, fish and cultivated meat. In this ...
Feb. 29, 2024 Leafy green vegetables are important sources of dietary fiber and nutrients, but they can harbor harmful pathogens. In particular, lettuce has often been involved in outbreaks of foodborne illness ...
Aug. 14, 2023 With climate change, irrigating more crops in the United States will be critical to sustaining future yields, as drought conditions are likely to increase due to warmer temperatures and shifting ...
Mar. 17, 2022 Marine cold spells are cold versions of heat waves: periods of exceptionally cold water, able to hurt or help the ecosystems they hit. Today, the oceans experience just 25% of the number of cold ...
Jan. 28, 2022 In the U.S., 52% of irrigated land is used for corn, soybean and winter wheat production. Corn and soybean are two of the country's most important crops, with 17% of corn production and 12% of ...
July 5, 2021 Bioenergy with Carbon Capture and Storage (BECCS), a negative emission technology, has been considered inevitable to achieve the 2°C or 1.5°C climate goal. Although numerous studies have been ...
