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November 17, 2020

The Mystery Behind Seasonality – A Leafy Green Issue?

Shiga toxin-producing Escherichia coli (STEC) outbreaks in 2018 and 2019 linked to leafy greens have raised many questions regarding recurring STEC outbreaks. Until 2018 when the U.S. Food and Drug Administration (FDA) and the Centers of Disease Control and Prevention (CDC) presented their analysis of eight years-worth of data to industry, it was largely unknown that seasonality seemed to be playing a role in STEC outbreaks associated with leafy greens. When and how have transition periods between growing leafy green regions become periods of vulnerability to STEC contamination? What is known and what is being done to address recurring outbreaks associated with leafy greens, namely romaine lettuce?

To answer these questions Western Growers Science hosted and led a two-part Seasonality Webinar Series in September 2020 in collaboration with the Arizona and California Leafy Green Marketing Agreements (LGMAs). The webinars, gathering a total of 276 registrants, were meant to increase awareness and share industry efforts to prevent leafy greens outbreaks during transition periods in California (September-November) and in Arizona (March-May).

What is ironic is that leafy greens grown under the AZ and CA LGMAs—about 90% of the leafy greens grown in the U.S.—follow stricter food safety practices than those required under the Produce Safety Rule (PSR) and other industry commodity-specific guidelines. Since 2018, when the leafy green industry was made aware of potential seasonality issues, many practices and procedures have changed for the industry. Being a leafy green producer in 2020 is quite different than what it was a decade ago.

Research suggests outbreaks are most likely not caused by one risk factor or hazard, but a combination of conditions and events that create a “perfect storm.” To decrease the likelihood of a “perfect storm” materializing, leafy green growers have implemented many new requirements. The LGMA-approved leafy green food safety practices have been updated 18 times since they were first developed in 2007; in some cases, there was more than one update each year. Numerous changes have been made to the LGMA in the last year; however, logistical and practical considerations must still be taken into account and, as appropriate, changes implemented.

A 2019 report by Dr. Gregory Astill of the USDA Economic Research Service demonstrated that USDA’s daily shipments data can be used in outbreak investigations involving romaine lettuce to estimate the specific timeframe of the outbreak. Currently, there are industry and government supported research efforts aimed at finding the root cause of this pattern of seasonality in leafy green outbreaks. In addition to water source quality, surrounding land use and crop products applied in the off-season, some of the factors under examination include risks associated with domestic and wild animal movement, changes in farm management as production slows down, and weather-related changes that may impact bacterial growth.

Despite all the additional requirements from LGMA revisions and new insights from research and data analyses, the leafy green industry continues to be under a lot of pressure. In the FDA’s 2020 Leafy Greens STEC Action Plan, the agency discusses its activities focused on three areas: prevention, response, and knowledge gaps. Many of these activities are underway and more continue to be announced. A few weeks ago, FDA’s Office of Regulatory Affairs initiated intensive testing in the Salinas area as part of the Action Plan targeting certain leafy green growing operations as part of their outbreak follow-up investigations. In addition, the agency recently resumed a one-year sampling assignment for romaine lettuce, which was on hold due to COVID-19 considerations. More details about the assignment can be found on the FDA website.

In addition to FDA’s domestic actions, foreign regulatory activity has also become quite intensive. Since October 7, romaine lettuce imported into Canada from specific California counties are subject to new requirements. These new requirements implemented by the Canadian Food Inspection Agency will be in effect until the end of 2020 and can be found on their website. Because the new requirements were enacted only five days after the official announcement, there was very limited opportunity for us to engage in the process. Moreover, the timing of these new control measures is not amenable to broad and straightforward adoption by all supply chain participants, so trade has been significantly impacted.

Co-existence is perhaps a topic for another story, but it should not be ignored, since pathogens can be transferred or come from other agricultural activities in the same region and can certainly also explain how crops may be more susceptible to contamination during transition periods. If you are a grower, please contact the Western Growers’ Science team to see how you can become engaged on different initiatives to advance science-based food safety practices. If you are not a leafy green grower, please know that leafy green operations are working diligently while under a lot of pressure to address what some call the “mystery behind seasonality.”