The FDA has started sampling Salinas Valley lettuce for Shiga toxin-producing E. coli and Salmonella species as part of online surveillance efforts following recurrent outbreaks linked to the products grown in this region. E. coli O157:H7 outbreaks linked to these products, more specifically romaine lettuce, have occurred in 2020, 2019, and 2018.
Romaine lettuce is uniquely susceptible to contamination because of the way it grows. The lettuce grows in a cup shape very close to the ground. That shape can collect and hold irrigation water, which can be contaminated with pathogens, especially if the farm field is located near factory cattle farms. There is a recurring strain of E. coli O157:H7 in the region that has been identified in leafy greens year after year.
In this new surveillance program, sampling will be conducted at many different cooling and cold storage facilities where field heat is removed from the lettuce,e and where the leafy greens are stored before they are processed. Sampling may include pre-cooled product, which investigators prefer, or post-cooled product.
This sample collection helps the FDA obtain samples from multiple farms at centralized locations. It also helps facilitate proper traceback to the farm and follow-up with the grocer if any contamination is detected in the greens.
The FDA is going to collect and test about 500 post-harvest samples of iceberg, leaf, and romaine lettuce. Each sample will consist of 10 subsamples. Each subsample is one head of lettuce that is trimmed, cored, and may be wrapped. For romaine lettuce, each sample will be loose leaves or one package of hearts. FDA labs will conduct all of the testing.
During this assignment, the FDA will take “extra precautions” to help make sure the investigators and employees are safe during the COVID-19 pandemic. Their visits to the farms and collection centers will be pre-announced, and the investigators will be outfitted with personal protective equipment.
The safety of leafy greens is a high FDA priority. Other work is underway, in collaboration with stakeholders in the California Central Coat growing region to identify where the recurring strain of E. coli is persisting, along with the likely routes of contamination.
