US: Count of generic Escherichia coli on spinach at the preharvest level determined by the multi-factorial effect of ambient temperature, precipitation, farm management and environmental factors
American Society for Microbiology: 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. 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 generic E. coli on spinach is determined by weather only.