Purpose: The objective of this study was to develop a system model that simulates the effect of animal feces as a source of contamination in leafy greens, and to conduct a sensitivity analyses to determine the impact of different levels of animal feces on contamination of leafy greens.
Methods: A system model consisting of subsystems and inputs to the system (soil, irrigation, cattle, swine, and rainfall) simulating a hypothetical farm in the Salinas Valley was developed. For sensitivity analyses, the levels of contamination in the baseline model were increased and decreased by up to 100% at intervals of 20% (i.e., ±20%, ±40%, ±60%, ±80%, and ±100%).
Results: At the level of a 100% increase in swine defecation, the mean value of E. coli in the harvested crops increased by 1.66- to 4.56-fold compared with the level in the baseline model. When swine defecation was decreased by 100%, the decrease in the mean values was in the range of 1.66- to 11.62-fold. Similarly, when the runoff was increased by 100%, the increase in the mean populations of E. coli in the crops was 1.45- to 7.17-fold. The mean population of E. coli in the crops was predicted to decrease by 2047- to 8822-fold during April to June and by 1.64- to 6.86-fold during July to November, when the runoff was decreased by 100%.
Significance:
These results could be useful in developing metrics to mitigate the risks of leafy greens associated outbreaks.