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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