Southwest Agricultural Region Environmental Microbiology Study on Foodborne Pathogens (2019 – 2024)

In 2019, the FDA, in collaboration with the University of Arizona and others, began a multi-year study in Yuma County, Arizona. The study was designed to improve understanding of the environmental factors that may impact the presence of foodborne pathogens in the Southwest agricultural region. The researchers were particularly interested in identifying new information about factors that significantly contribute to the introduction, persistence, growth, spread, and die-off of pathogens that could contaminate the produce before harvest in this region.

Airborne transmission of viable STEC

was documented numerous times at several locations adjacent to and incremental distances from a nearby large livestock and composting operation (80,000+ cattle). In addition, air, water, and lettuce leaf microbiome analysis demonstrated deposition of dust from cattle pens to the nearby water and land, suggesting that dust from CAFOs (Concentrated Animal Feeding Operations) may play a role in STEC transmission in this part of the region. These findings indicate that STEC can survive in the air and that dust can act as a transfer mechanism for pathogens and indicator organisms (e.g., generic E. coli) from adjacent and nearby land to water, soil, and plant tissue. Additionally, distance played an essential factor in the likelihood of STEC being detected in collected airborne dust, with the percentage of positive samples declining steadily as air sampling moved away from concentrated animal operations.


Water Quality

The research team repeatedly observed that generic E. coli concentrations and STEC prevalence and isolation frequency increased as irrigation canal water flowed past an adjacent livestock and compost operation. In addition, these changes in water quality occurred without other explanations, such as surface run-off or other direct contamination, which indicates that the airborne disposition of dust from a nearby CAFO was potentially a factor in the contamination of the irrigation water. Similar findings were not observed from samples obtained concurrently from a nearby irrigation canal that flows south of the CAFO and associated compost operation. This suggests the critical role of localized southerly winds in transferring CAFO-associated dust in northward directions.


Wildlife Contributions


Over 1,000 samples of wildlife fecal material, including from a wide variety of mammals and birds, were collected to study the role wildlife in this region may contribute to pathogen dissemination. Emphasis was placed on birds, both native and migratory, given their presence and ability to access terrestrial areas, including produce fields and livestock areas, as well as various surface water locations, including irrigation canals. Over 40 bird species were sampled, with red-winged blackbirds being the only species testing positive for STEC in very few of the nearly 60 samples collected from this bird species. Therefore, 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 risks to production, the environment, and water sources.


Whole genome sequencing results

More than 40 different STEC serotypes were recovered from roughly 500 samples representing all the matrices examined in this study. STEC strains detected in water, sediment, and plant tissue harvested from our research plots genetically matched strains isolated in air samples, providing evidence that bacteria in air can transfer to other locations and surfaces.


Post-Study Actions

The preliminary results of this study stress the interconnectedness between people, animals, and the environment and serve as an essential model for how to foster productive dialogue among diverse stakeholders to improve food safety. Just as collaboration across the Southwest agricultural community was critical to the development and execution of this study, continued collaboration among stakeholders including livestock managers/producers, fresh produce growers, academia, extension, retailers, and federal, state, and local government partners will be important to help control and mitigate potential contamination via environmental transmission including air/dust from adjacent and nearby land.

Members of the Arizona leafy greens industry will be working through the Desert Food Safety Coalition to continue to collaborate with the Arizona Department of Agriculture, University of Arizona Extension, Yuma Fresh Vegetable Association, Yuma Safe Produce Council, Arizona Farm Bureau, Arizona Leafy Green Marketing Agreement (AZ LGMA), Western Growers, USDA-APHIS Wildlife Services, Arizona Cattle Feeders’ Association, additional grower and landowner coalition members and other agricultural community stakeholders to engage the industry and inform best practices to improve food safety in the region.


While the results are regionally specific, they may also help us address some knowledge gaps identified in the Leafy Green STEC Action plan, particularly concerning Adjacent and Nearby Land Use. As additional data analysis is completed, the FDA plans to engage with stakeholders to explore further the data and information gathered from this study.

The research team intends to present additional details about this study during the International As final data analysis occurs, we intend to publish manuscripts on this in the scientific literature. Additional information and publications will be added to this page as they become available.



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