Managing leafy green safety from adenoviruses and enteroviruses in irrigation water

Irrigation water regulations use Escherichia coli as an indicator of fecal contamination. However, it is well documented that bacterial indicators may not be ideal for predicting viral pathogen presence. Viral pathogens survive relatively long periods in water, are resistant to treatment processes, and cause a large number of illnesses annually. Therefore, this study explored the application of quantitative microbial risk assessment (QMRA) to understand adenovirus and enterovirus concentration limits in irrigation water to achieve an acceptable annual risk estimate of 1 infection per 10,000 exposures. A two-step approach was used to define target viral concentrations: 1) a risk model describing infection from consuming irrigated leafy greens and 2) optimization of the risk model using Monte Carlo simulation to define viral concentrations with an output risk value of 1 × 10⁻⁴. Our QMRA estimates target concentrations for adenoviruses and enteroviruses would be 6.9 × 10⁻³ and 1.5 genome copies/100 mL irrigation water, respectively. Improving the accuracy of the risk model will require a more robust survey of enteric viruses in irrigation waters and dose-response models specific for adenoviruses and enteroviruses present throughout the farm-to-fork continuum. This research contributes to the important step of adapting irrigation water monitoring practices to more accurately represent viral pathogens’ role in foodborne outbreaks.