Dirty water, warm trucks, and the real reason romaine keeps making us sick

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."