Given the size of the outbreak, at least 218 in the US and Canada, and the number of unnamed farms and fields implicated, I am not surprised that the source of the outbreak was broad environmental contamination – like water.  As a study that was performed in the Yuma growing area from 2007-2009 said: “Despite the fact that Arizona leafy greens has never been associated with foodborne outbreaks, this study is contributing with relevant information that can be used for future regulatory guidelines”.  Well, that clearly has changed. Survey of Selected Bacteria in Irrigation Canal Water – Third Year_0

This outbreak appears to be over as of June 28, 2018.

Epidemiologic, laboratory, and traceback evidence indicated that romaine lettuce from the Yuma growing region was the likely source of this outbreak.

The FDA and state and local regulatory officials traced the romaine lettuce to many farms in the Yuma growing region. The FDA, along with CDC and state partners, started an environmental assessment in the Yuma growing region and collected samples of water, soil, and manure. CDC laboratory testing identified the outbreak strain of E. coli O157:H7 in water samples taken from a canal in the Yuma growing region. WGS showed that the E. coli O157:H7 found in the canal water is closely related genetically to the E. coli O157:H7 from ill people. Laboratory testing for other environmental samples is continuing. FDA is continuing to investigate to learn more about how the E. coli bacteria could have entered the water and ways this water could have contaminated romaine lettuce in the region.

As of June 27, 2018, 210 people infected with the outbreak strain of E. coli O157:H7 were reported from 36 states. Illnesses started on dates ranging from March 13, 2018 to June 6, 2018. Ill people ranged in age from 1 to 88 years, with a median age of 28. Sixty-seven percent of ill people were female. Of 201 people with information available, 96 (48%) were hospitalized, including 27 people who developed hemolytic uremic syndrome, a type of kidney failure. Five deaths were reported from Arkansas, California, Minnesota (2), and New York.  (PHAC) identified 8 ill people in several Canadian provinces infected with the same DNA fingerprint of E. coli O157:H7. On June 22, 2018, PHAC reported that the outbreak in Canada appears to be over.