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  5. Microbiological Surveillance Sampling: FY22-23 On-Farm Inspections and Sampling of Leafy Greens Grown in the Salinas Valley, CA, Region
  1. Sampling to Protect the Food Supply

Microbiological Surveillance Sampling: FY22-23 On-Farm Inspections and Sampling of Leafy Greens Grown in the Salinas Valley, CA, Region

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Seeking to gain insight into foodborne illness outbreaks involving leafy greens, the U.S. Food and Drug Administration (FDA) and the California Department of Food and Agriculture (CDFA) conducted coordinated sampling and inspections at 14 farms in the Salinas Valley, CA, agricultural region during the 2022 harvest season. CDFA conducted the inspections, and the FDA conducted the sampling.

The FDA selected the farms from the results of unresolved traceback investigations[1] from 2020 to 2021, with the goal of ascertaining the source(s) of the outbreaks, if possible. Additionally, the objectives of the agencies’ 2022 inspections and sampling in the Salinas Valley agricultural region were to identify potential contamination of leafy greens and to prevent contaminated or potentially contaminated product from entering commerce. During these field activities, conducted from July to October of 2022, the two agencies also continued their efforts to better educate growers to help them adhere to the FDA’s Produce Safety Rule.

CDFA performed the inspections under the FDA-State Produce Safety Implementation Cooperative Agreement Program, a partnership established to provide technical and financial assistance to state and territorial agencies to develop and implement produce safety programs and to help ensure compliance with the Produce Safety Rule.

All samples collected during the 2022 work in the Salinas Valley region were tested for E. coli O157:H7, a type of Shiga toxin-producing E. coli (STEC), and Salmonella spp., both of which can cause severe illness. This work was a part of the FDA’s Leafy Greens STEC Action Plan, an ongoing preventive effort to help ensure the microbiological safety of leafy greens in the United States.


Outbreaks of foodborne illness involving leafy greens linked to or potentially linked to the Salinas Valley region have continued to occur, with at least one such outbreak occurring in each of the past five years.[2] The Salinas Valley region produces roughly 70 percent of the lettuce grown in California.[3] Leafy greens are among the most commonly consumed vegetables in the American diet and are typically eaten without undergoing a ‘kill step,’ such as cooking, to reduce or eliminate pathogens.

In 2021, consistent with the FDA’s prevention efforts, the agency conducted an assignment to collect lettuce from commercial cooling operations that service the Salinas Valley region to test for the presence of E. coli O157:H7 and Salmonella spp. The FDA detected non-O157 STEC and Salmonella during its 2021 assignment. Those findings, considered alongside the outbreaks, indicated to the FDA that further surveillance was warranted, but more focused on farms potentially linked to the outbreaks.

As a next step, the FDA planned inspections and sampling of farms[4] identified in unresolved traceback investigations from 2020 to 2021 as potentially associated with outbreaks of foodborne illness wherein leafy greens were the likely or suspect food vehicle. The two complementary activities, conducted during the Salinas Valley leafy greens harvest season, were envisioned to provide more complete insights into the microbiological risks to leafy greens at the identified sites.

[1] A traceback investigation is the method used to determine and document the production and distribution chain as well as the source(s) of a product that has been implicated in a foodborne illness investigation.

[2] FDA Center for Outbreak Response and Evaluation (CORE): Public Health Advisories from Investigations of Foodborne Illness Outbreaks. The “past five years” refers to 2018 to 2022.

[3] USDA: 2017 Census of Agriculture – Table 29

[4] The entities identified by the traceback investigations may be best characterized as “farm businesses.” The traceback investigations identified entities that in many cases owned or contracted for the use of more than one parcel of farmland. Additionally, all the farms (or entities) encompassed more than one field.

[5] The FDA and CDFA use three terms to classify inspectional outcomes: Official Action Indicated (OAI), Voluntary Action Indicated (VAI), and No Action Indicated (NAI). An “OAI” classification indicates significant violations and is accompanied by regulatory action. A “VAI” classification indicates lesser violation(s).

[6] “Preliminary Indication” suggests a sample may yield a final result that could indicate a public health threat. Analytical testing remains ongoing and final results have not yet been determined.

[7] CDFA inspected this farm on July 28, 2022. The inspectional outcome was NAI. The FDA collected the sample about two months following the inspection (on September 26, 2022).

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