Abstract
Produce-related foodborne illnesses are a significant public
health burden. It is critical to identify routes of
fecally-associated contamination in produce in the agricultural
production environment to design appropriate interventions aimed at
preventing the introduction of microbial contamination on farms.
The study goals were to quantify microbial contamination in soil,
water, hand rinse, and produce rinse samples for four microbial
indicators (E. coli, Enterococcus spp., fecal
coliforms, and somatic coliphages) and to assess the relationship
between microbial contamination in produce rinses and soil, water,
and hand rinse samples. Produce rinse samples (N=279) were
collected from farms and packing sheds and matched to soil (N=81),
water (N=164) and hand rinse samples (N=196) during the 2011 and
2012 growing seasons. Samples were processed by enumerative methods
for E. coli, Enterococcus spp., fecal coliforms, and
somatic coliphages. We used bivariate analysis, multivariate linear
models, and logistic models to evaluate the relationship between
produce rinse samples and environmental samples for all four
microbial indicators. Our findings showed low levels of
contamination in soil and water samples and a lack of association
between soil and water contamination and produce contamination. We
also found a high proportion of positive samples in hand rinses and
a significant association between concentration of microbial
indicators in hand rinse samples and concentration in produce rinse
samples (β=0.17-0.57, 95% CI=0.03-0.69). Consistent with
prior studies, farms in this study employed techniques that carry a
lower risk of microbial contamination including the irrigation of
produce with well water from irrigation drip-tape hoses and the use
of synthetic fertilizer covered by plastic mulch. Mechanistically,
the relationship between hand and produce contamination may be
explained by effective microbial adherence and transfer as well as
repeated contact between hands and produce. These results highlight
the need for interventions surrounding farmworker hygiene and
sanitation to interrupt microbial adherence and persistence on
farmworkers hands.
Table of Contents
Chapter 1: Comprehensive Review of the Literature ...1
Burden of Produce-Related Foodborne Illnesses... 1
Common Foodborne Pathogens Associated With Produce ...3
Fecal Indicators as a Proxy for Foodborne Pathogen Contamination...
4
Sources of Produce Contamination on Farms ...6
Detection Methods ...11
Goal ...12
Significance ...13
Chapter 2: Manuscript.. 14
Introduction... 14
Methods... 17
Study area ...17
Sample collection... 17
Produce rinses ...18
Water ...19
Soil ..19
Hand rinses ...20
Microbial indicator testing ...20
Statistical Analyses... 22
Results... 24
Discussion ...28
Strengths and Limitations... 35
Tables and Figures... 36
Chapter 3: Conclusion and Recommendations ...41
Conclusion... 41
Recommendations ...42
References ..44
Appendices ...52
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