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Epidemiologic Analysis and Risk Management Practices for Reducing E. Coli in Irrigation Source Water Supplies and Distribution Systems


We propose to conduct a detailed statistical and epidemiological analysis of irrigation water data being collected by the produce industry in order to identify risk management practices and remediation measures that reduce generic E. coli in irrigation water supplies. <P>
We will also determine the feasibility of changing the rate of water sample testing for low- or high-risk irrigation water sources. Our first task will be to develop an advisory committee comprised of members from organizations such as the Center for Produce Safety, United Fresh Produce Association, Western Growers Association, California LGMA, California Leafy Greens Research Program, Salinas Valley Grower-Shipper Association, Produce Marketing Association, and commercial laboratories. Our 2-year project will complete the following objectives:
Objective 1. Finalize master data file. In collaboration with CPS, growers and commercial labs, the master data file will be updated, enhanced, and compared against the goals of objectives 2 through 5 to resolve data gaps. Data will include date of sample, generic E. coli value, water chemistry, type of water source, geographical region, sampling location along the irrigation distribution system, and diagnostic method. Additional environmental, operational and structural risk factors will be identified for inclusion in the data file under confidentiality agreements. We will also add precipitation, ambient temperature, and wind velocity for each geographical region.
Objective 2. Risk factors for measurable E. coli. Using logistic regression (prevalence) and negative binomial regression (concentration), we will identify environmental, geographical, structural and operational conditions and diagnostic methods associated with the occurrence of generic E. coli in irrigation water. This will help the produce industry identify risk factors and diagnostic procedures associated with elevated prevalences and higher concentrations of generic E. coli in irrigation water supplies at different points along their distribution.
Objective 3. Risk factors for E. coli exceedances. Using mixed effects logistic regression (prevalence), we will identify predisposing environmental, structural, and operational risk factors associated with generic E. coli exceedances in irrigation water supplies.
Objective 4. Mitigation measures for E. coli. Using mixed effects logistic regression (prevalence), we will test the ability of different mitigation measures used by growers to reduce the reoccurrence of an E. coli exceedance in their irrigation water supplies.
Objective 5. Efficient use of water testing resources. Using the binomial distribution to calculate the probability to detect E. coli occurrences as a function of water sample testing rate and risk-level of the water source, this analysis will determine if low- or high-E. coli risk source water supplies can be sampled using lower or higher rates of sampling in order to maximize the efficiency of a water testing plan. In addition, we will evaluate if seasonal data suggest that certain times of year can be sampled more efficiently using higher or lower rates of sampling.

<P>This project will assist the produce industry comply with current LGMA microbiological standards for generic E. coli in irrigation water supplies, avoid E. coli exceedances by identifying effective remediation measures, and develop efficient irrigation water sampling plans for low- to high-risk irrigation water sources.

Harris, Linda; Atwill, Edward
University of California - Davis
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