The likelihood that a crop of leafy greens will be contaminated by E. coli, an indicator of fecal contamination, before harvest is strongly influenced by both farm management and environmental factors, according to a study spotlighted on the cover of the new issue of the journal Applied and Environmental Microbiology.

The work, led by Dr. Renata Ivanek and her lab in the Department of Veterinary Integrative Biosciences (VIBS) at the Texas A&M College of Veterinary Medicine & Biomedical Sciences (CVM), was a collaborative effort between researchers at Texas A&M University, Colorado State University, Texas Tech University, and Texas A&M AgriLife Extension Service.

In this study, the research team cross-referenced environmental data with information from participating farms in multiple test areas. Then, the team determined how three groups of factors—farm management, location, and weather—affect spinach contamination with E. coli. The team studied spinach samples from 12 farms in Colorado and Texas and compared variables including the local temperature, precipitation, wind speed, soil characteristics, proximity to roads and water bodies, and such farm management practices as the farm workers’ hygiene and manure application practices.

Overall, the study found that farm management, location, and weather factors should be considered jointly in developing agricultural methods and interventions that reduce the threat of E. coli contamination at the pre-harvest level. The odds of spinach contamination decreased to approximately 1 in 17 with implementation of good hygiene practices for farm workers, but they increased to approximately 4 in 1 for every millimeter increase in the average amount of rain in the month before harvest. Furthermore, applying manure fertilizer on the field increased the odds of contamination to approximately 52 in 1.

“Hygiene practices and fertilizers used are relatively easy to change,” Ivanek said. “The challenge, however, will be to use the information about how rainfall affects produce safety into an intervention, or plan, that growers could implement on a daily basis.”