Abstract
The burden of foodborne disease attributed to fresh produce in
the U.S. is substantial in terms of costs and human health
implications. Currently, Mexico is one of the major traders of
produce with the U.S., and therefore it is important to understand
the nature of this relationship as it relates to food safety.
However, few epidemiological studies have assessed the routes by
which microbial contamination is introduced into the food chain
during production of fruits and vegetables. It is essential to
identify these routes in order to implement targeted food safety
interventions and ultimately reduce foodborne illnesses. The study
goals were to evaluate the effects of production step on microbial
concentration and prevalence of fecal indicator organisms on
high-risk produce (cantaloupe melons, jalapeño peppers,
and tomatoes) and farm workers' hands over multiple growing seasons
from 2010-2011. Produce samples (n=254) and farmer workers' hand
rinses (n=171) were collected from 11 farms and packing sheds near
the U.S.-Mexico border and enumerated by culture methods for E.
coli, fecal coliforms, Enterococcus spp., and somatic
coliphages. Linear regression and logistic regression modeling
approaches were employed to quantify differences in microbial
quality of produce and hands at different production steps. The
final packing shed step, melons, and year of sample collection were
significantly and positively correlated with fecal indicator
concentration and prevalence on produce. However, contamination was
still present, but at significantly lower concentrations in the
field steps, indicating that contamination may originate in the
field and be amplified in the packing shed, especially for melons.
Both regression methods produced estimates of similar direction and
significance. In summary, the packing shed step, melons, and year
of sample collection were significantly associated with microbial
concentrations on produce. This investigation highlights several
potential routes of produce contamination in the production
environment and demonstrates the need to implement food safety
interventions in packing shed facilities on produce farms, as well
as the need for extra care be taken to adequately clean melons
prior to shipment.
Table of Contents
INTRODUCTION 1
PRODUCE AS A FOODBORNE DISEASE VEHICLE 1
Changing National Food Consumption Patterns 1
Challenges in Food Safety Policy 2
Production Processes as Introduction Points of Contamination
3
Fecal Indicators as Models for Pathogen Contamination 4
Previous Research Group Findings 5
Research Goal 6
MATERIALS AND METHODS 7
Description of Field Conditions and Agricultural Practices in
Production Process 7
Produce Sample Collection 8
Farm Workers' Hand Rinse Sample Collection 9
Microbial Analysis 9
Microbial Quantification 10
Statistical Analysis 12
RESULTS 14
Descriptive Statistics 14
Model Construction 14
Linear Model Results 15
Produce 15
Hands 17
Logistic Model Results 19
Produce 19
Hands 21
DISCUSSION 23
Packing Shed as Production Step of Concern for Microbial Quality of
Produce and Workers' Hands 24
Significantly Different Microbial Quality of Melons Between
Production Steps 26
Positive Non-Linear Pattern of Fecal Indicator Contamination
Throughout Production Steps Indicate that Contamination Present in
Field Steps 29
Year of Sample Collection as Statistically Significant Predictor of
Microbial Quality 29
Comparison of Linear and Logistic Regression Results 30
Strengths and Limitations of Study 31
Conclusions, Future Studies, and Public Health Implications
33
REFERENCES 36
TABLES 44
FIGURES 56
APPENDIX 61
About this Master's Thesis
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