The U.S. Food and Drug Administration (FDA) and collaborators have shared preliminary key findings from a multi-year environmental study in Yuma County, Arizona—a major producer of leafy greens in the U.S. The findings include data analyses on airborne pathogens, water quality, wildlife contributions and whole genome sequencing results.

The purpose of the study was to gain a better understanding of the ecology of foodborne pathogens in the environment in the Southwest growing region. Specifically, the research team aimed to uncover new insights into the factors that significantly contribute to the “introduction, persistence, growth, spread, and die-off of pathogens that could contaminate produce prior to harvest in this region.”

The study was in collaboration with the University of Arizona, the Wellton-Mohawk Irrigation and Drainage District, local growers, industry groups and other stakeholders and was conducted between May 2019 and April 2024. Throughout the five-year period, researchers collected environmental samples across an estimated 54-mile area within the Southwest agricultural region and observed fluctuations in the types and prevalence of pathogens over time, location and seasonality.

The preliminary key findings have been updated on the FDA’s website here, and a summary of the findings are below:

• Shiga toxin-producing E.coli (STEC) strains detected in water, sediment and plant tissue genetically matched strains isolated in air samples, providing evidence that STEC in air can transfer to other locations and surfaces.
• Air samples collected during the study yielded positive viable pathogen results indicating that bacteria can survive in the air and that dust can act as a transfer mechanism for both pathogens and indicator organisms (e.g. generic E. coli) from adjacent and nearby land to water, soil and plant tissue. Distance played an important factor in the likelihood of STEC being detected in collected airborne dust, with the percentage of positive samples declining steadily as air sampling moved in an incremental manner away from concentrated animal operations.
• Surface water evaluated in the study experienced a change in water quality and an increase in the prevalence of STEC as water moved past a nearby Concentrated Animal Feeding Operation (CAFO), even in the absence of surface run-off or other direct contamination, which indicates that airborne disposition of dust from the CAFO was potentially a factor in the contamination of the irrigation water.
• Birds and other wildlife do not appear to be significant sources of STEC or E. coli O157:H7 in or around the part of the Southwest growing region evaluated. However, continued monitoring is warranted to reduce potential risk to produce, the environment and water sources.

The research team will present more details about the study at the International Association for Food Protection annual meeting, taking place on July 14-17, 2024.

The California Department of Food and Agriculture (CDFA) issued the following statement:

The study highlighted below was initiated following a 2018 E. coli O157:H7 outbreak linked to romaine lettuce from the Southwest growing region and represents one of the largest environmental microbiology research efforts to date. Multi-year environmental studies are designed to shed light on environmental conditions that could impact food safety. Having this kind of study helps reinforce the shared commitment to public health through research, science and continuous improvement to promote science-informed food safety practices.

California continues to remain engaged in food safety discussions through the diverse stakeholders represented by the California Agricultural Neighbors (CAN) efforts and by way of the California Longitudinal Study. While the study mentioned below is unique to the Southwest growing region, a One Health approach recognizes the health of people, animals and the environment are intertwined with the goal of achieving holistic health outcomes. You can learn more about California’s One Health efforts related to produce safety on the CDFA Produce Safety One Health Initiatives webpage.

The Industry Advisory Group closely involved with the initial research effort aims to reconvene under the Desert Food Safety Coalition, which includes Western Growers. Western Growers is dedicated to advancing food safety both in our industry and at home. We will persist in our efforts to collaborate with agricultural stakeholders, engage the industry and share best practices to enhance food safety. This is a region-specific study. If you have any concerns about the findings, food safety compliance or your organization’s food safety plan, please contact me at [email protected].