Evaluating norovirus contamination of fresh produce on US and Mexican farms and mitigating SARS-CoV-2 risk among essential food workers Restricted; Files Only

Sobolik, Julia (Spring 2023)

Permanent URL: https://etd.library.emory.edu/concern/etds/s4655h990?locale=en


Within the US agricultural sector, food workers are critical for producing safe, nutritious food and for distributing this food to consumers. Moreover, the agricultural sector is responsible for providing high-quality, contamination-free foods to ensure consumer safety. In this dissertation, we use quantitative microbial risk assessment (QMRA) and infectious disease modeling (IDT) approaches to investigate within the agriculture environment, transmission dynamics associated with SARS-CoV-2 and human norovirus, two pathogens that affect workers and the food supply.

Food workers have been disproportionately affected by SARS-CoV-2. In AIM 1, we developed a QMRA model to simulate: 1) individual and cumulative SARS-CoV-2 infection risks from close contact, aerosol, and fomite-mediated exposures; and 2) relative reduction in SARS-CoV-2 infection risk attributed to control interventions. We found bundled interventions reduced worker risk to below 1% for an 8h exposure.

Detection of SARS-CoV-2 on frozen food packaging has raised concerns for possible surface-mediated transmission. In AIM 2, we used a QMRA model of a cold-chain facility to simulate SARS-CoV-2 fomite-mediated infection risks following contact with contaminated packaging. We found the SARS-CoV-2 risk from contact with plastic packaging was quite low. Handwashing and masking practices further reduced risk by 99.4%.

Norovirus is the leading cause of produce-associated foodborne outbreaks in the U.S. In AIM 3, we evaluated the individual and combined effect of farm-based hand hygiene and worker furlough practices on produce-associated norovirus infection. Washing hands frequently and well effectively reduced norovirus risk to consumers; across all commodities bundled interventions effectively reduced risks.


The impact of farm-level norovirus contamination events on human health remains unclear. We developed in AIM 4 a QMRA-linked IDT model to characterize: 1) individual risk from consumption of norovirus-contaminated tomatoes, and 2) theoretical disease dynamics in a population given a norovirus seeding event. We found heterogeneity in norovirus risks across age, genetic susceptibility, and viral characteristics. At the population-level, distinct outbreak patterns emerged, which were dependent on key model assumptions (infectious to non-infectious ratio, seeding amount).


Using context-specific modeling approaches, this dissertation seeks to advance the evidence-base for effective infection control strategies to ensure the health of workers and consumers in the agricultural environment.

Table of Contents

Chapter 1 Introduction 1

1.1 U.S. agriculture sector: healthy workers and consumers1

1.1.1 Protecting frontline worker health and safety2

1.1.2 Protecting consumer health4

1.2 Utility of the quantitative microbial risk assessment (QMRA) framework to evaluate infectious disease exposures in the agricultural environment6

1.3 Norovirus IDT and QMRA-IDT models8

1.4 Dissertation Aims10

1.4.1 Research Aim 110

1.4.2 Research Aim 211

1.4.3 Research Aim 312

1.4.4 Research Aim 413

1.5 References14

Chapter 2 AIM 1 Controlling risk of SARS-CoV-2 infection in essential workers of enclosed food manufacturing facilities24

2.1 Abstract25

2.2 Highlights26

2.3 Introduction27

2.4 Materials and Methods29

2.5 Results39

2.6 Discussion47

2.7 Conclusions55

2.8 Funding56

2.9 Acknowledgements57

2.10 Figures and Tables57

2.11 References62

2.12 Chapter 2 AIM 1 Supplementary Information68

Chapter 3 AIM 2 Decontamination of SARS-CoV-2 from Cold-Chain Food Packaging Provides no Marginal Benefit in Risk Reduction to Food Workers87

3.1 Abstract88

3.2 Highlights89

3.3 Introduction90

3.4 Materials and Methods91

3.5 Results and Discussion95

3.6 Conclusions98

3.7 Funding99

3.8 Acknowledgements100

3.9 Figures and Tables101

3.10 References113

3.11 Chapter 3 AIM 2 Supplementary Information119

Chapter 4 AIM 3 Norovirus transmission mitigation strategies during simulated produce harvest and packing 131

4.1 Abstract132

4.2 Highlights133

4.3 Introduction134

4.4 Materials and Methods135

4.5 Results143

4.6 Discussion148

4.7 Acknowledgements and Funding155

4.8 Figures and Tables155

4.9 References163

4.10 Chapter 4 AIM 3 Supplementary Information168

Chapter 5 AIM 4 Application of a novel QMRA-IDT model to investigate individual and population-level norovirus transmission dynamics from contaminated tomatoes in the agricultural environment 184

5.1 Abstract185

5.2 Highlights187

5.3 Introduction188

5.4 Materials and Methods190

5.5 Results199

5.6 Discussion205

5.7 Acknowledgements and Funding211

5.8 Figures and Tables212

5.9 References216

5.10 Chapter 5 AIM 4 Supplementary Information223

Chapter 6 Summary, limitations, implications, and future directions237

6.1 Summary of findings237

6.2 Limitations240

6.3 Implications244

6.4 Future directions247

6.5 Conclusions251

6.6 References252

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