The objective of this study was to determine the effects of farm management and environmental factors on preharvest spinach contamination with generic Escherichia coli as an indicator of fecal contamination. A repeated cross-sectional study was conducted by visiting spinach farms up to four times per growing season over a period of 2 years (2010 to 2011). Spinach samples (n ‫؍‬ 955) were collected from 12 spinach farms in Colorado and Texas as representative states of the Western and Southwestern United States, respectively. During each farm visit, farmers were surveyed about farm-related management and environmental factors using a questionnaire. Associations between the prevalence of generic E. coli in spinach and farm-related factors were assessed by using a multivariable logistic regression model including random effects for farm and farm visit. Overall, 6.6% of spinach samples were positive for generic E. coli. Significant risk factors for spinach contamination with generic E. coli were the proximity (within 10 miles) of a poultry farm, the use of pond water for irrigation, a >66-day period since the planting of spinach, farming on fields previously used for grazing, the production of hay before spinach planting, and the farm location in the Southwestern United States. Contamination with generic E. coli was significantly reduced with an irrigation lapse time of >5 days as well as by several factors related to field workers, including the use of portable toilets, training to use portable toilets, and the use of hand-washing stations. To our knowledge, this is the first report of an association between field workers' personal hygiene and produce contamination with generic E. coli at the preharvest level. Collectively, our findings support that practice of good personal hygiene and other good farm management practices may reduce produce contamination with generic E. coli at the preharvest level.

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A repeated cross-sectional study was conducted to identify farm management, environment, weather, and landscape factors that predict the count of generic Escherichia coli on spinach at the preharvest level. E. coli was enumerated for 955 spinach samples collected on 12 farms in Texas and Colorado between 2010 and 2012. Farm management and environmental characteristics were surveyed using a questionnaire. Weather and landscape data were obtained from National Resources Information databases. A two-part mixed-effect negative binomial hurdle model, consisting of a logistic and zero-truncated negative binomial part with farm and date as random effects, was used to identify factors affecting E. coli counts on spinach. Results indicated that the odds of a contamination event (non-zero versus zero counts) vary by state (odds ratio [OR] ‫؍‬ 108.1). Odds of contamination decreased with implementation of hygiene practices (OR ‫؍‬ 0.06) and increased with an increasing average precipitation amount (mm) in the past 29 days (OR ‫؍‬ 3.5) and the application of manure (OR ‫؍‬ 52.2). On contaminated spinach, E. coli counts increased with the average precipitation amount over the past 29 days. The relationship between E. coli count and the average maximum daily temperature over the 9 days prior to sampling followed a quadratic function with the highest bacterial count at around 24°C. These findings indicate that the odds of a contamination event in spinach are determined by farm management, environment, and weather factors. However, once the contamination event has occurred, the count of E. coli on spinach is determined by weather only. Foodborne disease outbreaks associated with produce impose a considerable public health burden (1). Among different produce commodities, leafy green vegetables have been identified as a group of high concern from a microbiological safety perspective due to their being implicated in multiple outbreaks of foodborne disease with high numbers of illnesses worldwide (2). Indeed, leafy green vegetables are commonly grown in open farm fields, where they may be exposed to microbial contamination from soil, manure fertilizer, irrigation water, and intrusions of wild or domestic animals, and they are likely to be consumed fresh or minimally processed. Enteric foodborne pathogens, such as Salmonella and Escherichia coli O157:H7, have been the main causative agents responsible for foodborne outbreaks associated with leafy green vegetables in the United States (3). These pathogens are spread in the environment through feces of infected animals and humans (4). While contamination of leafy greens with these foodborne pathogens has major consequences (2), fortunately it occurs at a low frequency (5, 6). The low frequency and heterogeneous distribution of these pathogens in the produce field make their detection difficult, costly, and time-consuming. Instead indicator organisms are routinely used by the industry, environmental agencies, and public health organizations to verify effective implementation of good ag...