Identifying causative factors contributing to positive leafy green samples. (rapid response)

While there have been numerous studies and programs designed to mitigate the occurrence of microbial pathogens in leafy greens, particularly in California, there has been no strong linkage made between the mitigation practices and actual microbial pathogen occurrence. This is especially the case for pathogen levels observed that may not result in illness if the produce is consumed. Absent those linkages, it is unclear if best practices are contributing to reduced disease causing microbial pathogen levels and if so, the significance of the contribution. This proposal seeks to identify the causative factors that may contribute to the occurrence of pathogens in leafy greens using data obtained from a survey coordinated among industry participants in the Salinas Valley. In this project, a database will be created that over time can become the reference point for improving best practices. This work is intended as a pilot program designed for implementation during the 2011 Salinas Valley growing season. Future work will build on this database and may result in a data-intensive leafy green risk assessment. To ensure the proposal objectives meet industry needs, we will work with a leafy green sample group (LGSG) consisting of processors, handlers and growers, who contribute individual field data to subsequently to create a database containing 2011 case control survey data.

This proposal consists of six primary objectives: 

1.) prepare a data management plan 2.) formalize the agreement with individual company participants 3.) obtain company data and populate the database 4.) analyze the data for correlations between pathogen occurrences and individual practices/practice failures 5.) review the findings with participants 6.) complete a final report.

Findings An analysis of the data reveals potential correlations between positive product tests and several variables: field proximity to grazing land (although the correlation is counter intuitive), irrigation type (furrow irrigation), and weather, particularly rainfall and humidity. Given the small number of positive samples, the data should be considered preliminary. However, the findings are useful and warrant further data collection for confirmation. Critical to the success of the project is the ability to collect sufficient numbers of case and control surveys. During the 2011- fall 2013 growing season, there were few “positives”, limiting our ability to collect additional surveys responses. Therefore, a program collecting this type of data needs to run for several years to obtain enough survey responses for statistical validity. As for the pilot program, the importance of the research was not only to determine if the data could be collected and then to collect it and analyze it, but also to determine the program limitations in order to make improvements in any future study. Based on the observations during the pilot program, several improvements can be made going forward. First, a consistent methodology for the selection of case and control sites needs to be adopted by all companies for statistical purposes. Consistent sampling patterns and protocols need to be used by all companies. Finally, the program would benefit from one individual completing all surveys for all companies to ensure consistency. Recommendations We recommend CPS continue its support of the case-control program as a means of collecting sufficient data to make a determination of the causative factors contributing to positive leafy green samples. Acknowledgement We would like to thank the companies and their employees supporting this project.