Understanding the relationship between norovirus and indicator organisms on predicted contamination of produce along the United States-Mexico border 公开

Abstract

Previous research has shown that norovirus is the primary cause of foodborne outbreaks in the United States and that of foodborne illnesses caused by viruses in particular, norovirus accounts for almost all cases of illnesses. Common sources of food contamination are grower’s hands, produce contamination in the field, and hands of workers preparing food for the consumer.

Norovirus is preventable, but challenges include: viral persistence on surfaces, low concentrations in samples, and lack of field and cost friendly detection methods. Typically, indicator organisms, which are microbes that are present in fecal contamination and easier to detect, are used to decide if pathogen presence in a sample is likely. Research to understand the relationship between presence of bacterial and viral indicators and presence of norovirus on different environmental samples is needed. This study aims to determine if bacterial and viral indicators can inform the presence of norovirus on grower’s hands, produce, and in water of crops grown along the US-Mexico border.

From 2011-2012, hand-rinse, soil, water (source and irrigation), and produce (melons, jalapeños, tomatoes) samples were taken from 11 farms. Each sample was assayed for indicators: E. coli, coliforms, Enterococcus, Bacteroidales, and coliphages. Intra-indicator relationships were evaluated by sample type using a Spearman rank-correlation test. Norovirus presence was examined by testing a subset of 50 samples and reporting proportions of samples positive for either norovirus genotype GI or GII. Logistic models and odds ratios were calculated to determine if there was a relationship between indicator presence and norovirus presence (a=0.05).

When E. coli was present on produce, there was a significant relationship with coliforms (OR=24.54; p=0.0285), Enterococcus (OR=2.84; p=0.0012), and coliphages (OR=2.34; p=<0.0001). No other indicators had significant relationships with other indicators. By sample type, Enterococcus showed strong, significant relationships with coliphages (rho=0.6242) and coliforms (rho=0.6251) on produce samples. Norovirus was present on 6/50 (12%) samples, five of which were positive for genotype II. Of the samples positive for norovirus, 50% were from source water, 33% from hand-rinses, and 17% from produce. There was no relationship between norovirus presence and any of the indicators tested. Overall, the low proportion of samples positive for norovirus and the absence of a relationship between norovirus and any indicator implies that these indicators are not a good predictor of norovirus contamination.

Table of Contents

Table of Contents

Literature Review............................................................................................................1

Data and Methods...........................................................................................................12

Study Sites......................................................................................................................12

Study Design...................................................................................................................13

Statistical Analyses.........................................................................................................15

Results.............................................................................................................................17

Descriptive Statistics.......................................................................................................17

Assessing the presence, quantity, and relationship of indicators....................................17

Assessing the presence of norovirus................................................................................19

Assessing the relationship between indicator and norovirus presence...........................19

Discussion........................................................................................................................21

Intra-indicator Relationships...........................................................................................21

Norovirus Presence..........................................................................................................22

Relationship between Indicators and Norovirus..............................................................23

Implications.....................................................................................................................25

References........................................................................................................................26

Figures and Tables............................................................................................................38

Table 1. Proportion of positive samples and mean concentration of log-transformed variables for indicator microbes and norovirus, entire sample and stratified by sample type......................................................................................................................38

Table 2. Intra-Indicator Relationship based on Presence for entire sample—Odds Ratio, (95% confidence interval), p-value..................................................................................................................................39

Table 3. Correlation Matrix for Intra-Indicator Relationship based on Concentration for sample type—Spearman correlation.........................................................................................................................39

Table 4. Proportion of Samples positive for Norovirus by sample type and produce type....................................................................................................................................40

Table 5. Relationship between indicator presence and norovirus presence for entire sample—Odds ratio (95% Confidence Interval), p-value...................................................................................................................................40

Appendix A: IRB Approval..................................................................................................41

About this Master's Thesis

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School	Rollins School of Public Health
Department	Hubert Department of Global Health
Degree	M.P.H.
Submission	Master's Thesis
Language	English
Research Field	Environmental Health Health Sciences, Public Health
关键词	public health food safety produce contamination environmental health norovirus
Committee Chair / Thesis Advisor	Leon, Juan, Emory University
Committee Members	Prince-Guerra, Jessica, Emory University

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