And, they forgot the eight sick in Canada.
I shortened it a bit and bolded the highlights.
In early April 2018, the Food and Drug Administration (FDA), in conjunction with the Centers for Disease Control and Prevention (CDC) and state partners, began to investigate a multi-state outbreak of E. coli O157:H7 infections. When this outbreak was declared over by the CDC two months later, it was the largest outbreak of E. coli O157:H7 infections in the United States since 2006, with 210 reported illnesses from 36 states, resulting in 96 hospitalizations, 27 cases of hemolytic uremic syndrome (HUS) and five deaths.
Traceback of the romaine lettuce consumed by ill people determined that it originated in the Yuma produce growing region which consists of farms in Imperial County, California, and Yuma County, Arizona. The traceback identified a total of 36 fields on 23 farms in the Yuma growing region as supplying romaine lettuce that was potentially contaminated and consumed during the outbreak. With the exception of one instance where one of the legs of the traceback led to a single farm, it was not possible to determine which, or how many, of these farms shipped lettuce that was contaminated with the outbreak strain of E. coli O157:H7.
The epidemiological and traceback analyses performed during this outbreak informed an FDA-led Environmental Assessment (EA) of the Yuma produce growing region in collaboration with CDC and state partners from June through August 2018. The EA was conducted to assist FDA in identifying factors that potentially contributed to the introduction and spread of the outbreak strain of E. coli O157:H7 that contaminated the romaine lettuce associated with this outbreak.
The EA team made several visits to the Yuma growing region to conduct its work. During these visits, the team collected numerous environmental samples. Three of these samples were found to contain E. coli O157:H7 with the same rare genetic fingerprint (by whole genome sequencing) as that which made people sick. These three samples were collected in early June from a 3.5 mile stretch of an irrigation canal near Wellton in Yuma County that delivers water to farms in the local area, including several identified in the traceback as having potentially shipped romaine lettuce contaminated with the outbreak strain.
The romaine lettuce that ill individuals consumed was likely harvested between early March and mid-April 2018 based on the fact that reported illness onset dates occurred from March 13 – June 7, 2018. The traceback indicates that the contaminated lettuce had to have been grown on multiple farms and processed at multiple off-farm fresh-cut produce manufacturing/processing facilities.
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.
Information collected by the EA team indicates that, among the Yuma area farms identified in the traceback and that were interviewed, irrigation canal water was only directly applied during germination. However, aerial and ground-based spraying of crop protection pesticides diluted with irrigation canal water occurred at various times during the growing season on a number of these farms, including after a freeze event that occurred in late February. This freeze event likely led to damage of some portion of the romaine lettuce crop, which may have rendered it more susceptible to microbial contamination.
It is uncertain how the outbreak strain of E. coli O157:H7 was introduced into this 3.5-mile stretch of irrigation canal water. The first illnesses in this outbreak occurred in March 2018, and therefore the outbreak strain may have been present in the irrigation canal months before the EA team collected the positive samples, or the outbreak strain may have been repeatedly introduced into the irrigation canal. A large concentrated animal feeding operation (CAFO) is located adjacent to this stretch of the irrigation canal. The EA team did not identify an obvious route for contamination of the irrigation canal from this facility; in addition, the limited number of samples collected at the CAFO also did not yield the outbreak strain.
Low-level E. coli O157:H7 contamination of the romaine lettuce from some of the growing fields identified in the traceback could have been amplified by commingling cut romaine lettuce in wash systems at fresh-cut produce manufacturing/processing facilities. Washing of romaine lettuce either at a fresh-cut produce manufacturing/processing facility or at home by consumers may reduce but will not eliminate pathogens, including STEC, from romaine lettuce. The commingling of romaine lettuce from various farm growing fields at fresh-cut produce manufacturing/processing facilities complicated traceback efforts and made it impossible for FDA to definitively determine which farm or farms identified in the traceback supplied romaine lettuce contaminated with the E. coli O157:H7 outbreak strain.
FDA recommends that growers and processors of leafy greens:
- assure that all agricultural water (water that directly contacts the harvestable portion of the crop) used by growers is safe and adequate for its intended use (including agricultural water used for application of crop protection chemicals);
- assess and mitigate risks related to land uses near or adjacent to growing fields that may contaminate agricultural water or leafy greens crops directly (e.g. nearby cattle operations or dairy farms, manure or composting facility);
- verify that food safety procedures, policies and practices, including supplier controls for fresh-cut processors, are developed and consistently implemented on farms (both domestic and foreign) and in fresh-cut produce manufacturing/processing food facilities to minimize the potential for contamination and/or spread of human pathogens;
- when a foodborne pathogen is identified in the growing or processing environment, in agricultural inputs (e.g., agricultural water), in raw agricultural commodities or in fresh-cut ready-to-eat produce, a root cause analysis should be performed to determine the likely source of the contamination, if prevention measures have failed, and whether additional measures are needed to prevent a reoccurrence; and
- Local in-depth knowledge and actions are critical in helping resolve potential routes of contamination of leafy greens in the Yuma growing region, including Imperial County and Yuma County moving forward. FDA urges other government and non-government entities, produce growers and trade associations in Yuma and Imperial Counties to further explore possible source(s) and route(s) of contamination associated with the outbreak pathogen and with other foodborne pathogens of public health significance. This information is critical to developing and implementing short- and long-term remediation measures to reduce the potential for another outbreak associated with leafy greens or other fresh produce commodities.