P3-56 Pathogen Prevalence and Indicator Organism Levels in Three Open Surface Water Systems in Washington

Wednesday, July 25, 2012
Exhibit Hall (Rhode Island Convention Center)
Karen Killinger, Washington State University, Pullman, WA
Craig Cogger, WSU, Pullman, WA
Andy Bary, WSU, Pullman, WA
Achyut Adhikari, Washington State University, Pullman, WA
Katherine Warren, Washington State University, Pullman, WA
Sean Beckman, Washington State University, Pullman, WA
Elaine Brouillard, RSBOJC, Sunnyside, WA
Introduction: Understanding pathogen risk associated with irrigation water is an important aspect of produce food safety.

Purpose:   To examine open surface waters as a potential source of microbial contamination for produce farming  systems, three water systems in Washington were monitored for pathogen presence and indicator organism levels over two years.

Methods: Sampling sites were selected based on stakeholder input to collect monitoring data that would be beneficial to local producers.  Site A (8 sampling sites and 18 sampling dates), Site B (14 sampling sites and 13 sampling dates) and Site C (16 sampling sites and 12 sampling dates) represented three different geographic regions in Washington.  Samples were quantified for fecal coliforms and generic Escherichia coli using a five-tube most probable number technique, and analyzed for pathogen presence (E. coli Ol57, Salmonella). Washington Department of Ecology (WA-DOE) utilizes a water quality standard for secondary contact recreation water of < 2.3 log colonies/100 ml fecal coliforms and the Leafy Greens Marketing Agreement (LGMA) recommends <2.37 log MPN/100 ml generic E. coli for foliar irrigation application.

Results: Pathogen prevalence (E. coli O157 and Salmonella) ranged from 5.2% (5 pathogen positives) at Site A to 6.9% (14 pathogen positives) at Site C.  At Site A, 5 pathogen positives were observed when both the WA-DOE fecal coliform standard and LGMA E. coli standard were met, and only 1 pathogen positive was observed when both standards were exceeded.  Alternatively, both Sites B and C had 5 pathogen positives observed when both WA-DOE and LGMA standards were exceeded.  Site B had 6 pathogen positives when only the WA-DOE fecal coliform standard was exceeded and Site C had 9 pathogen positives when only the WA-DOE fecal coliform standard was exceeded. 

Significance: Meeting indicator organism standards may not accurately reflect pathogen risk.  Emphasis on good agricultural practices and risk assessment for irrigation water management programs is warranted.