Source: Rita Jane Gabbett, MEATINGPLACE, 12/2614


Current leafy green field distance guidelines of 120 meters (400 feet) may not be adequate to limit the transmission of E. coli O157:H7 to produce crops planted near concentrated animal feeding operations, according to a new study.

The study, titled, “Effect of Proximity to a Cattle Feedlot on Escherichia coli O157:H7 Contamination of Leafy Greens and Evaluation of the Potential for Airborne Transmission” was published in Applied and Environmental Microbiology. An abstract was posted on the American Society for Microbiology website.

Lead author of the study is Elaine Berry, a researcher at  USDA’s Agricultural Research Service, U.S. Meat Animal Research Center, in Clay Center, Nebraska. 

The impact of proximity to a beef cattle feedlot on E. coli O157:H7 contamination of leafy greens was examined. In each of two years, leafy greens were planted to nine plots located 60, 120, and 180 meters from a cattle feedlot (3 plots each distance).

Leafy greens (270) and feedlot manure samples (100) were collected six different times from June to September in each year.
Both E. coli O157:H7 and total E. coli were recovered from leafy greens at all plot distances. E. coli O157:H7 was recovered from 3.5 percent of leafy green samples per plot at 60 meters, which was higher than the 1.8 percent of positive samples per plot at 180 meters, indicating a decrease in contamination as distance from the feedlot was increased.

Although E. coli O157:H7 was not recovered from air samples at any distance, total E. coli was recovered from air samples at the feedlot edge and all plot distances, indicating that airborne transport of the pathogen can occur.

Results suggest that risk for airborne transport of E. coli O157:H7 from cattle production is increased when cattle pen surfaces are very dry, and when this situation is combined with cattle management or cattle behaviors that generate airborne dust.

“Current leafy green field distance guidelines of 120 meters (400 feet) may not be adequate to limit the transmission of E. coli O157:H7 to produce crops planted near concentrated animal feeding operations,” the authors wrote. “Additional research is needed to determine safe set-back distances between cattle feedlots and crop production that will reduce fresh produce contamination.”

The research was conducted because incidents of foodborne disease outbreaks caused by contamination of fresh produce are rising.

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