Pathogenic contamination of tomatoes, cantaloupe, and jalapenos on farms in Coahuila and Nuevo Leon, Mexico Open Access

Abstract

Produce-associated outbreaks contribute to healthcare costs and societal well-being. Risk for produce-related outbreaks is increasing due to globalization. The goal of this study was to assess the presence and association of indicators on produce with environmental samples on farms by aiming to quantify the extent of indicators on produce and their environmental samples and to discover associations between the environmental exposure variables (soil, irrigation water, and hands) and the outcome variable (produce) using indicators to determine presence of fecal material. Samples were tested for fecal coliforms, E. coli, Enterococcus, and Coliphages. Samples were collected from farms in the Coahuila and Nuevo Leon regions of Mexico. SAS 9.3 was utilized to describe concentrations and prevalence of indicators on samples and model linear and logistic regressions. When quantifying the prevalence of indicators in environmental samples, we found that many of the exposure samples of soil, irrigation water, source water, and farm worker hands contained fecal indicators. When quantifying the concentrations of indicators on environmental samples, we found that hands and produce typically had higher mean concentrations of indicators compared to soil, irrigation water, and source water. We discovered that soil and irrigation water that contained fecal indicators before harvest were significantly associated with produce containing fecal indicators before harvest (βsoil= -1.887) (βwater = 0.862) (controlling for produce type). We also found that hands that contained fecal indicators after harvest, during distribution, and at the packing shed were associated with produce contaminated with fecal indicators (ORcol = 9.67) (ORE.coli = 6.24) (controlling for produce type). An implication of this study was that remediation practices could potentially focus on hand washing behavioral changes at all stages of harvest to improve the cleanliness of the produce.

Table of Contents

Literature Review .............................................................................................................................. 1 Background: ................................................................................................................................... 1 Pathogens Involved in Foodborne Illness and the Focus of the Clean Greens Study: ..................................... 4 Bacterial and Fecal Indicators: ........................................................................................................... 8 Transmission Routes: ....................................................................................................................... 11 Goals and Aims: .............................................................................................................................. 14 Significance: .................................................................................................................................. 14 Materials & Methods ........................................................................................................................ 16 Study farms and subjects: ................................................................................................................ 16 Sample collection: ........................................................................................................................... 16 Experimental procedures. .................................................................................................................. 17 Data Analysis and Statistical Methods: ................................................................................................ 18 Linear Regression: ........................................................................................................................... 19 Logistic regression: ......................................................................................................................... 20 Results ......................................................................................................................................... 22 Descriptive Results: ........................................................................................................................ 22 Regression Results: ......................................................................................................................... 26 Discussion ..................................................................................................................................... 31 Description Analyses: ...................................................................................................................... 31 Regression Analyses: ....................................................................................................................... 32 Strengths and Limitations: ............................................................................................................... 33 Conclusion and Implications: ............................................................................................................ 33 Reference List ............................................................................................................................... 35 Tables .......................................................................................................................................... 42 Appendix A: IRB CLEARANCE ..............................................................................................................49

About this Master's Thesis

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School	Rollins School of Public Health
Department	Epidemiology
Degree	MPH
Submission	Master's Thesis
Language	English
Research Field	Health Sciences, Public Health
Keyword	fecal coliforms enterococcus Mexico farm coliphage produce contamination irrigation frequency Public Health regression O157:H7 indicator listeria Clean Greens jalapeno salmonella hands E. coli soil norovirus tomato cantaloupe
Committee Chair / Thesis Advisor	Leon, Juan, Emory University
Partnering Agencies	Emory University schools, faculty or affiliated programs

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