Microbiological Surveillance Sampling Main Page

The U.S. Food and Drug Administration (FDA) is conducting a sampling assignment to collect and test leafy greens grown on farms/ranches in the Salinas Valley, California, region that have been linked to an outbreak of foodborne illness or an outbreak signal. The FDA is testing all samples for E. coli O157:H7, a type of Shiga toxin-producing E.coli (STEC), and Salmonella spp. The agency is conducting this regulatory assignment as part of the FDA’s Leafy Green STEC Action Plan, which calls for ongoing surveillance of leafy greens to prevent potentially contaminated leafy greens from entering commerce and to help farm/ranch management strengthen the microbiological safety of their operations.

The FDA plans to collect product samples and may collect environmental samples at some farms/ranches. With respect to the product samples, the agency will collect iceberg, leaf and romaine lettuce grown in the region. If lettuce is not available at a farms/ranch, the agency may collect other leafy greens, prioritizing spinach.

The Salinas Valley and Leafy Greens

The Salinas Valley region produces about 70 percent of the U.S. grown lettuce.[1] Leafy greens are some of the most consumed vegetables in the American diet but are typically eaten without undergoing a ‘kill step,’ such as cooking, to reduce or eliminate harmful bacteria. In recent years, 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 outbreak occurring every year for the past four years.[2] This assignment is part of the agency’s ongoing surveillance of leafy greens in the interest of protecting public health.

Questions and Answers

What samples will the FDA collect?

The product samples to be collected will consist of whole heads of lettuce (iceberg, leaf and romaine), untrimmed whenever possible, obtained directly from production fields within farms/ranches in the Salinas Valley agricultural region of California. The agency does not plan to collect trimmed, cored, wrapped or topped-and-tailed lettuce. If lettuce is not available at a farm/ranch, the agency may collect other leafy greens, prioritizing spinach. The FDA also may collect environmental samples (e.g., water, soil and scat) as appropriate

Will all Salinas Valley region farms/ranches be subject to sampling during this assignment?

No. Under this assignment, the FDA will collect samples only from farms/ranches identified by traceback investigation in recent years as being potentially associated with a foodborne illness outbreak in which lettuce or leafy greens were identified as the likely or suspect food vehicle.

When will the FDA collect the samples?

FDA field staff will collect samples from September 19 to October 30, 2022.

How many samples does the FDA plan to collect for this assignment?

The agency plans to collect up to 240 product samples in all, primarily lettuce but also including spinach or other leafy greens, if necessary. The agency will collect approximately one to four lettuce samples at each farm/ranch, depending on its acreage and the scope of the operation. Each lettuce sample will consist of 10 subsamples, and each subsample will consist of one whole head of lettuce, untrimmed whenever possible. Samples of other leafy greens likewise will consist of 10 subsamples. The FDA also may collect environmental samples as appropriate based on observations made at the time of sampling and a farm/ranch’s past inspection history.

How will the samples be collected?

The agency will notify the farm/grower of the collection visit typically a few days in advance. FDA field staff will seek to coordinate with and request the aid of farm/ranch personnel in harvesting product that the FDA field staff identify to sample. FDA field staff also will be prepared to harvest product themselves, as needed, and will collect samples using standard techniques set forth in the FDA’s Investigations Operations Manual (Chapter 4.3), which describes the use of sterile equipment and aseptic procedures.

Who will conduct the testing?

The FDA will test the samples at its laboratories in Alameda and Irvine, CA, Bothell, WA, and Denver, CO.

What regulatory action will the FDA take if it detects Salmonella spp. or E. coli O157:H7?

The FDA will notify the responsible party at the farm/ranch (typically, its owner or operator), and others identified by the farm/grower, with respect to the test results. The FDA will discuss with the farm/grower what voluntary action the farm/grower intends to take regarding the produce associated with the positive sample result. The FDA also will assess whether an on-farm, follow-up inspection is warranted and what actions may be needed to identify potential routes and sources of contamination. A follow-up inspection would seek to help the farm/ranch management identify practices or conditions that may present microbial risks so that they could improve the microbiological safety of their operation(s) and, ultimately, prevent potentially contaminated product from reaching consumers.

---

[1] USDA: 2017 Census of Agriculture – Table 29
[2] FDA - Public Health Advisories from Investigations of Foodborne Illness Outbreaks. Advisories by Year