June 24, 2022

FDA Releases Results of Romaine Lettuce Sampling Assignment

The FDA has released results of their romaine lettuce sampling assignment, which was instituted after years of Shiga toxin-producing E coli (STEC) outbreaks linked to that product. The FDA did not detect any pathogens during the assignment.

FDA Releases Results of Romaine Lettuce Sampling Assignment

Unfortunately, this is not unusual and doesn’t mean that there will not be any more outbreaks linked to romaine or leafy greens. Contamination can be spotty and can vary with weather conditions and the presence of animals in the field. Furthermore, it’s impossible to sample every leaf of romaine lettuce. E. coli bacteria tend to clump in small amounts and can be difficult to detect. It only takes 10 of these bacteria to make someone sick. And one head of contaminated lettuce can contaminate many bags of prepared lettuce.

In fact, the study stated, “The FDA cautions against making any further inferences based solely on this assignment’s findings given that the sample size was relatively small and in view of the fact that multiple foodborne illness outbreaks linked to romaine lettuce have occurred in recent years.”

The assignment was to detect pathogenic E. coli and Salmonella. The assignment began in November 2019 and ended in December 2020.There was a pause in the sample collection and testing from March through October 2020 due to the COVID-19 pandemic.

Unfortunately, that was the time frame when three “mystery” E. coli outbreaks were announced by the FDA. All three of those 2020 outbreaks may have been linked to romaine or leafy greens. One of the outbreaks was caused by a strain of E. coli that was genetically related to a strain associated with an outbreak in 2019 that were associated with romaine lettuce.

The agency prioritized collection at farms and FDA-registerd facilities that were identified in traceback investigations as suppliers of romaine that were possibly linked or were linked to outbreaks from 2017 to 2019. The FDA collected and teated 279 samples for both pathogens. Each sample was made up of 10 subsamples, with each subsample consisting of one or more heads or hearts of romaine lettuce.

The FDA says that this approach increases the probability of detecting pathogens if present, since the microbial hazards may not be uniformly precent. No fresh cut lettuce was collected, and no samples were collected from farm fields.

The samples were taken from wholesalers, distribution centers, on-farm holding locations, and commercial cooling and cold storage facilities. They were also taken, to a lesser extent, from refrigerated storage before consumer access at grocery stores.

Investigators did find E. coli in one sample, but lab analysis showed that that organism did not have any characteristics that would let it adhere to intestinal epithelium, which is essential for infection. Whole genome sequencing conducted on that pathogen determined it was not associated with any known human illnesses.

The FDA is going to continue to implement its action plan that was published last year, and will continue to work with farmers and distributors throughout the supply chain to strengthen the safety of leafy greens. The government has also launched two longitudinal studies in the lettuce growing regions of Arizona and California to understand how pathogens survive and migrate through the environment in those regions.

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