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Yuma Valley Growers Anticipating Season Free of Contamination


Growers in the Yuma, AZ valley were impacted by two consecutive outbreaks of E. coli O157:H7 during 2017 and 2018. Epidemiologic investigations indicated contamination of irrigation water emanating from concentrated animal feeding operations as the source of the pathogen. 


For the 2019 season, organizations in Arizona and California have established guidelines for growers.  The Leafy Greens Marketing Agreement requires buffer zones of 1,200 feet from any CAFO with many growers extending this distance.  A Wellton area feedlot adjacent to a three-mile length of the Wellton canal extending for 20 miles yielded the same E. coli as that isolated from patients applying whole genome sequencing assay.


The FDA traceback investigation 36 growing areas involving 23 farms as potential sources of contaminated romaine lettuce.  Although the specimens collected from the Wellton area feedlot in 2018 failed to yield the specific E. coli responsible for infection in consumers, it is acknowledged that excretion of a given strain can be variable. The number of samples collected late in the course of the outbreak was insufficient to establish statistically valid correlations between contamination of lettuce and the feedlots.  During August 2018, water samples from sections of the irrigation canal and from ground water failed to yield the infectious strain. Fields harvested at the end of the 2018 season have been plowed and have been exposed to sun and dry air that would be expected to kill E. coli if present.