Identification of Mitigation Measures to Prevent Norovirus Outbreaks in Indoor Food Production Facilities via Quantitative Microbial Risk Assessment Modeling Open Access

Flinn, Isabelle (Spring 2022)

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Norovirus is the leading cause of acute gastroenteritis in the United Sates with outbreaks of norovirus often linked to contaminated food. Infected food production workers may contaminate their work environment posing a risk of infection to their fellow workers. The purpose of this study was to quantify the cumulative risk of norovirus infection for a susceptible food production worker exposed to specific exposure events (fecal and vomit) and transmission pathways (fomite and aerosol). Additionally, the impact of mitigation measures (hand hygiene, surface disinfection, and masking) on the risk of norovirus infection for a susceptible food production worker were evaluated. A Quantitative Microbial Risk Assessment Model was created in R using the mc2d package for two-dimensional Monte Carlo simulation and was iterated over 10,000 simulations. Fomite and aerosol-mediated norovirus transmission pathways were examined for an infected worker experiencing either repeated fecal (fomite) or a single vomit (aerosol, fomite) event. In the absence of mitigation measures, the risk of norovirus infection associated with an 8-hour cumulative exposure varied by exposure event: fecal scenario (22%), and vomit scenario (0.53%). Compared to no mitigation measures, combined intervention utilization (hand washing, glove use, surface disinfection, and masking) resulted in a maximum reduction in the risk of infection of 99% in the fecal scenario and 96% in the vomit scenario. These findings provide insight into variation in the risk of norovirus infection by exposure event and transmission pathway, with exposure to norovirus contamination from fecal events posing the greatest risk. The findings of our model can be leveraged by the food production industry to minimize the infection risk associated with specific norovirus exposure events and transmission pathways through the prioritization of mitigation measures.

Table of Contents

1. Literature review 1

1.1 Norovirus burden of disease in the united states 1

1.2 Norovirus outbreaks 2

1.3 Implications of norovirus outbreaks among food workers 4

1.4 Transmission routes of norovirus 6

1.4.1 Foodborne transmission 6

1.4.2 Waterborne transmission 8

1.4.3 Fomite mediated transmission 8

1.4.4 Person-to-person transmission 9

1.4.5 Exposure routes relevant to food production activities on the produce production floor 10

1.5 Mitigation measures to protect workers from norovirus infection 11

1.6 Quantitative microbial risk assessment frameworks applied to worker health 12

1.7 Need, objectives, and significance of the present study 14

2. Methods 16

2.1 Model overview & structure 16

2.2 Data sources 18

2.3 Transmission from a fecal event 19

2.3.1 Contamination of infected worker hands and fomite reservoirs 19

2.3.2 Fomite transmission modeling 22 The restroom environment & production floor door handle 22 Product boxes 23

2.3.3 Viral dose 24

2.4 Transmission from a vomit event 25

2.4.1 Aerosol transmission modeling 26

2.4.2 Fomite transmission modeling 27

2.5 Interventions 30

2.6 Risk assessment 31

2.7 Sensitivity analysis 31

3. Modeling results 32

3.1 Risk of infection in fecal event module 32

3.2 Risk of infection in vomit event module 33

3.3 Effects of hand hygiene interventions on reducing infection risk 33

3.4 Effects of surface disinfection on reducing infection risk 34

3.5 Effects of surgical face mask use on reducing infection risk 35

3.6 Effects of combination intervention utilization on reducing infection risk 35

3.7 Sensitivity analysis 36

4. Discussion 38

4.1 Risk of norovirus infection differs by exposure event and transmission pathways 38

4.1.1 Risk of norovirus infection from exposure to repeated fecal events 40

4.1.2 Risk of norovirus infection from a vomit exposure event 40

4.2 Risk of norovirus infection is reduced differentially by intervention type 41

4.4 Modeling strengths, limitations, & future directions 45

4.5 Conclusions & public health recommendations 47

5. Bibliography 49

6. Tables and figures 61

Table 1. Parameters, Values, And Probability Distributions Used In The QMRA Models 61

Figure 1. Norovirus QMRA schematic for fecal and vomit exposure pathways 67

Figure 2. Risk of norovirus infection across two modeled exposure pathways 68

Figure 3. Reduction in norovirus infection risk attributed to hand hygiene interventions 69

Figure 4. Reduction in norovirus infection risk attributed to surface disinfection 70

Figure 5. Reduction in norovirus infection risk attributed to use of a surgical face mask 71

Figure 6. Reduction in norovirus infection risk attributed to use of combined interventions 72

Figure 7. Fecal event module spearman’s rho correlation coefficients 73

Figure 8. Vomit event module spearman’s rho correlation coefficients 74

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