Quantitative microbial exposure modelling as a tool to evaluate the impact of contamination level of surface irrigation water and seasonality on fecal hygiene indicator E. coli in leafy green production.

The use of Quantitative Microbial Exposure Assessment (QMEA) modelling of faecal hygiene indicator microorganisms (e.g. E. coli), is proposed as an alternative approach to the use of Quantitative Microbiological Risk Assessment (QMRA) models of enteric pathogenic microorganisms in the fresh produce chain. As more field data and quantitative microbial models become available, the potential use of QMEA models as a tool to assess the impact of different risk mitigation strategies increases helping growers to make the right decisions. This paper focuses on the pros and cons of previously published QMRAs as well as on the proposal of an alternative approach based on the use of a quantitative microbial contamination modelling to investigate how the selection of the irrigation water sources affect the E. coli loads in leafy greens at harvest. The modified model describes the final E. coli levels of baby spinach when different water sources with different contamination levels are applied and the impact of seasonality. Substantial differences were observed between the irrigation water sources while seasonality only had small effects on the simulated levels of E. coli in the harvested baby spinach. Based on the results, the produce grown using irrigation water from drainage ditches show E. coli levels above threshold levels (2 log CFU/g) while less than 1% of baby spinach irrigated with water obtained from water reservoirs where above this limit. The use of this QMEA model will help growers in the decision-making process to reduce microbial contamination of leafy greens.