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Scientifically valid corrective actions for multiple harvest shadehouse production systems


From 1996 to 2016, seven events of foodborne illness associated with the consumption of raw cucumbers have been reported. Six of the outbreaks were attributed to Salmonella spp., and one to E. coli, resulting in over 1200 illnesses and 260 hospitalizations. Outbreaks in the five most recent incidents attributed to cucumbers were grown in protected culture (3 Salmonella and 1 E. coli O157:H7) and one Salmonella outbreak in an open farm environment. In the final update of the large multistate outbreak of Salmonella enterica sv. Poona associated with consumption of fresh cucumber, CDC reported that more than 907 people from 40 states were infected with the outbreak strains of Salmonella Poona. Of these, 204 ill people were hospitalized, and six deaths directly attributed to the infection. The implicated cucumbers were grown in protected culture, specifically shade-houses. The outcomes of the on-going outbreak environmental investigation of S. Poona on cucumber boldly underscored the need to develop a specific science-basis for the critical decisions necessary by any shade-house producer and affiliated shipper to prevent or respond and recover in the event of a detected contamination on a multiple harvest crop. Similar to open-field poled or staked production systems, most protected culture involves crops with multiple harvests over at least a few months period. Within these production units, each standing crop at harvest maturity, and each harvested lot in distribution, is intimately linked to the remaining crop. A common response to a positive postharvest pathogen detection may be to destroy the remaining shade- house production as the practical economic loss containment decision; however, a better knowledge foundation for die-off expectations and systematic sampling regime may shift the risk burden to packing operations. At this time, there is very sparse science-based guidance for systematically assessing the risk of contamination of fresh produce grown under protected culture. Closing this knowledge gap is critical to decision-making and application of validated corrective actions in the case of presumptive or confirmed pathogen detection in preharvest product or environmental samples. Our goal is the validation of die-off expectations for bacterial pathogens and corrective action options for shade-house crops. To accomplish this goal we propose to determine the comparative die-off kinetics of indicator E. coli, attenuated Salmonella, attenuated shiga-toxin E. coli, and indicator Listeria innocua contaminants in controlled research shade-houses. We propose also to evaluate the efficacy of various corrective actions to minimize the risk of transference and persistence of bacterial pathogens within and on the standing crop. Environmental monitoring guidance will result from studies that comparatively evaluate sampling protocols, sample processing protocols, and detection sensitivity for bacterial pathogens. Overall, we proposed to elucidate system-wide improvements in preventive controls, environmental monitoring programs, and recall-response management for shade-house grown fruit vegetables and the development of science-based responses to routine monitoring and early detection of contamination events. We anticipate a high degree of transferability to other protected crop culture systems and multiple harvest crops.

Suslow, Trevor
University of California - Davis
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