FDA Can't Determine How E. Coli Got on Lettuce in Deadly Romaine Outbreak
WASHINGTON -- The E. coli outbreak that claimed five lives last spring and resulted in stores and restaurants temporarily removing romaine from the menu was traced back to a small stretch of irrigation canal in the Yuma, Ariz., region.
But, the Food and Drug Administration said today in its environmental assessment of the crisis that it remains a mystery to investigators how the irrigation canal was contaminated with the deadly bacteria or how that water contaminated the lettuce.
The Centers for Disease Control and Prevention declared the outbreak over by June 28; the last harvest from the Yuma region was April 16. By that time, two deaths from eating the lettuce had been reported in Minnesota, and there was one death each in Arkansas, California, and New York. Out of the 210 known infections reported in 36 states, 96 people were hospitalized and 27 developed a type of kidney failure. Illnesses connected to the same outbreak were also reported in several Canadian provinces.
Symptoms of E. coli infection vary, but often include severe diarrhea and stomach cramps along with vomiting.
The CDC detected E. coli at the time in canal water, and the FDA picked up the investigation to determine how the water and the lettuce were contaminated.
Investigators found the outbreak "in three samples of water collected along a 3.5 mile stretch of an irrigation canal in the Wellton area of Yuma County," the report said, but "no other environmental samples collected in the region yielded the outbreak strain."
"It is unknown whether contamination with the outbreak strain in this irrigation canal extended beyond the 3.5-mile stretch," the report added. "FDA considers that the most likely way romaine lettuce became contaminated was from the use of water from this irrigation canal, since the outbreak strain of E. coli O157:H7 was found in the irrigation canal and in no other sampled locations. How this process occurred is uncertain, but based on interviews with growers and pesticide applicators, plausible explanations include direct application of irrigation canal water to the lettuce crop or the use of irrigation canal water to dilute crop protection chemicals applied to the lettuce crops through both aerial and land-based spray applications."
Still, the FDA "cannot rule out that there are other sources or means of romaine lettuce contamination that were not identified" during the investigation.
The report says investigators are "uncertain" as to how the E. coli "was introduced into this 3.5-mile stretch of irrigation canal water." Though a concentrated animal feeding operation is located next to the canal, investigators "did not identify an obvious route for contamination of the irrigation canal from this facility" and samples collected at the facility did not match the outbreak strain.
"Other possible explanations for how the irrigation canal became contaminated are possible, but the [environmental assessment] team found no evidence in support of alternative explanations," the report added.