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Numerous produce associated outbreak investigations (tomatoes, lettuce, spinach, cantaloupe) over the last 3-4 years have resulted in findings suggestive of preharvest contamination. A likely route of preharvest contamination of produce is through contaminated water. Potential sources of contaminated water include: 1) irrigation water contaminated by mixing with feces from untreated/improperly treated manure used to fertilize crops, 2) flooding of produce fields from upstream wash off from grazing or wild animals, and 3) agricultural water used for mixing pesticides/fungicides. <P> The objectives of this project are to determine whether E. coli O157:H7 is present in watersheds associated with raw produce production, when and where it is concentrated, the types of strains present, their relatedness, and their association with farm animals and birds.
Approach: In collaboration with California Central Coast Regional Water Quality Control Board (CCRWQCB), we will analyze water samples collected at least twice a month from the Salinas and Santa Maria watersheds in Monterey County for a minimum of one year. Additional samples (twice a week) will be collected during periods of intensive rainfall (more than one half of an inch). Additional sample covariates (possibly including fecal coliform levels, pH, turbidity, BOD, and ORP) will also be prioritized and measured. Guidance as to where samples will be obtained, and the watersheds to be sampled, will be determined in conjunction with CCRWQCB. The California Dept. of Health Services (CDHS) will provide additional samples (e.g. sediment, plant, feces) for analysis to attempt to trace the source of contamination when positive E. coli O157:H7 samples are detected. All sample locations and results will be encoded using GIS based mapping software. During these studies, improvements in methods for isolation and detection will be developed and tested in parallel with conventional methods for some samples. Positive samples will be confirmed by a variety of techniques including immunochemical and genetic methods, then fingerprinted by pulsed field gel electrophoresis and multilocus variable tandem repeat analysis (MLVA) methods.