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  1. Sampling to Protect the Food Supply

Microbiological Surveillance Sampling: FY16-17 Cucumbers

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The U.S. Food and Drug Administration (FDA) set out to collect and test cucumbers in 2015 under the agency’s new proactive and preventive approach to deploying its sampling resources with the ultimate goal of keeping contaminated food from reaching consumers.

The approach, detailed in the Background section of this report (page 5), centers on the testing of a large number of samples of targeted foods over a relatively short period, about 18 months, to ensure that enough data are available to inform decisions. This approach may help the agency determine if there are common factors – such as origin, variety or season – associated with pathogen findings.

The FDA issued the cucumbers assignment in November 2015 under its then new sampling model. The agency collected 1,601 samples to test to determine the prevalence of Salmonella spp. and Escherichia coli (E. coli) O157:H7 in the commodity. The agency collected about 76 percent of its samples from imported cucumbers and the rest from domestically produced cucumbers, comparable to their respective U.S. market shares at the start of the assignment. The agency designed its sampling plan such that if contamination of one percent or greater was present in the commodity, the agency would be likely to detect it. The agency monitored the assignment closely to gather lessons learned and to make changes to its sampling procedures if needed to address trends or food safety issues.

The FDA collected cucumbers grown in fields and greenhouses, with all varieties of the commodity eligible to be sampled. The agency did not collect frozen, chopped, sliced, pureed or pickled cucumbers, or those that it knew to be intended for a ‘kill step’ to eliminate pathogens. The agency found the prevalence of Salmonella in the samples collected to be 1.75 percent, based on the test results. The FDA did not detect E. coli O157:H7 (or other pathogenic E. coli) in any samples.

Consistent with the FDA’s mission to protect consumers, this assignment helped identify cucumbers as the vehicle in an outbreak of salmonellosis that involved 10 people in three states in 2016. Three patients were hospitalized during the outbreak, which is summarized in the Public Health Impact section of this report (page 12).

When the FDA detected Salmonella in domestic samples, the agency worked with the firm(s) that owned or distributed the affected cucumbers to conduct a voluntary recall, although in some cases there was no product to recall, or low likelihood of product available to recall due to the commodity’s relatively short shelf life. In instances where no recall was carried out, the agency provided the firm with guidance on minimizing microbial hazards in fruits and vegetables and shared its findings with state partners (as is done with samples that result in recalls).

When the FDA detected Salmonella in samples collected at ports of entry, the agency refused to admit the lot(s) associated with the positive samples and, where the criteria were met, placed the responsible firm(s) and product on Import Alert 99-23, “Detention without Physical Examination of Produce Due to Contamination with Human Pathogens.” In all, the agency placed seven firms on the import alert as a result of this sampling assignment. The agency also conducted intensified screening (i.e., additional sampling) of cucumbers from 10 foreign firms whose products tested positive at entry. One voluntary recall was conducted by an importer.

The findings of this assignment affirm that Salmonella may be present on cucumbers and so underscore the need for growers and others in the distribution chain to comply with the FDA’s Produce Safety Rule,[1] as applicable, and for importers to comply with the FDA’s Foreign Supplier Verification Programs Rule,[2] as applicable. Cucumbers require appropriate protection from human pathogens during growing, harvesting, packing and holding. The FDA intends to engage cucumber growers and distributors to make them aware of the findings of this assignment and to provide additional information on resources on steps to mitigate for contamination of cucumbers.

Consumers can take simple steps to reduce any possible microbial risks related to the consumption of cucumbers. Foodsafety.gov recommends that consumers “wash all produce thoroughly under running water before eating, cutting or cooking.” The site also advises, “Even if you plan to cut the rind or peel off the produce before eating, it is still important to wash it first so dirt and bacteria aren’t transferred from the knife onto the fruit.” The site furthermore advises consumers to scrub firm produce (including cucumbers) with a clean produce brush, and then dry it with a clean cloth towel or paper towel to further reduce bacteria that may be present.

The FDA will continue to evaluate methods to prevent microbial contamination of cucumbers. Such contamination remains a concern to the agency given this assignment’s findings and the history of outbreaks associated with cucumbers. Salmonella is able to survive on cucumbers past their recommended shelf life at refrigeration temperatures.[3] Additionally, cucumbers are a ready-to-eat food, meaning consumers do not typically subject them to a kill step (such as cooking) prior to consumption.

The FDA will continue to sample cucumbers for pathogens. Cucumbers are covered produce under the Produce Safety Rule, and among its next steps, the agency and its state partners began inspections of large produce farms for compliance with the Produce Safety Rule in the spring of 2019. ;The agency also will continue to sample imported cucumbers, including targeted sampling of product from countries of interest. With respect to the sampling of imported product, the FDA will use its PREDICT tool, which identifies shipments of interest based on certain risk criteria, to target future cucumber sampling efforts. In addition, the FDA will sample cucumbers using its longstanding approach to food sampling, which centers on (but is not limited to) the following criteria:

  • A firm has a history of unmitigated microbial contamination in the environment (e.g., as evidenced by being a confirmed source of human illness, recalled or seized product, prior inspectional history, or environmental pathogens without proper corrective actions by the facility), or
  • Inspectional observations that warrant collection of samples for microbiological analyses.

Employing the approaches described above, the FDA will sample cucumbers as warranted and take other steps consistent with its mission to protect consumers.


[1] The Produce Safety Rule establishes, for the first time, science-based minimum standards for the safe growing, harvesting, packing, and holding of fruits and vegetables grown for human consumption.

[2] The Foreign Supplier Verification Programs Rule requires that importers perform certain risk-based activities to verify that food imported into the U.S. has been produced in a manner that meets applicable U.S. safety standards.

[3] Bardsley, C. A., Truitt, L. N., Pfunter, R. C., Danyluk, M. D., Rideout, S. L., & Strawn, L. K. (2019). Growth and Survival of Listeria monocytogenes and Salmonella on Whole and Sliced Cucumbers. Journal of Food Protection, Vol. 82, No. 2, 301 to 319.