Quantifying the Risk of SARS-CoV-2 Infection in Essential Food Workers: A Quantitative Microbial Risk Assessment Approach Público
Cooper, Derrick (Spring 2021)
Published
Abstract
Essential food and agricultural workers in the United States experience an elevated risk of SARS-CoV-2 infection and mortality due to potential occupational exposures during produce harvesting or packaging. Furthermore, seasonal and migrant farmworker populations commonly rely on employer-provided shared lodging facilities and carpooling behaviors to arrive at their place of employment. The purpose of this study was to quantify the daily risk of SARS-CoV-2 infection for essential food workers from exposures throughout four relevant scenarios (shared transportation, shared lodging, outdoor harvesting field, indoor packaging facility). Additionally, the impact of CDC COVID-19 guidelines (face mask utilization, physical distancing) and existing FSMA requirements (handwashing, glove utilization, surface disinfection) as risk reduction strategies were also assessed. A quantitative microbial risk assessment (QMRA) model was created in R using a two-dimensional Monte Carlo package and 10,000 simulations. Aerosol, close-contact droplet, and fomite-mediated SARS-CoV-2 transmission pathways were examined based on the size distribution of droplets containing infectious SARS-CoV-2 released from an infected index case while coughing and the distance between an infected and susceptible worker (1, 2, or >3m). Without any mitigation strategies, the risk associated with each scenario included: 1h shared transportation (55.1%), 10h residential lodging (90.2%), 12h indoor packing facility shift (12.9%), and a 12h outdoor harvesting shift (14.9%). Relative to no intervention, mask use reduced infection risk by 69.2-82.7% (cloth), 78.5-88.8% (surgical), or 99.5-99.8% (N95) across all scenarios. Furthermore, surface disinfection reduced fomite-mediated transmission when applied daily (4.2%), bi-hourly (89.4%), or hourly (99.9%) in the indoor facility. Overall, these findings highlight the variable risk of SARS-CoV-2 infection across each scenario, with the residential and transportation scenarios resulting in the greatest risk of potential infection, while occupational risks are comparably lower.Across all scenarios, fomite-mediated infection risk remained negligible. These results highlight the potential risks associated with common practices in the agricultural sector (shared lodging, carpooling behaviors) while emphasizing the effectiveness of face mask and physical distancing interventions. Industry stakeholders can leverage these findings during policy creation (limiting shared contact between workers) and targeted risk reduction analyses (focusing on high-risk scenarios), to create a safer living and working environment for essential food workers.
Table of Contents
TABLE OF CONTENTS
1. LITERATURE REVIEW ............................................................................................................................................ 1
1.1 CHARACTERIZATION OF ESSENTIAL WORKERS ............................................................................................................. 2
1.2 TRANSMISSION ROUTES OF SARS-COV-2 ..................................................................................................................... 6
1.3 APPLICATIONS OF QUANTITATIVE MICROBIAL RISK ASSESSMENTS (QMRA) ................................................................. 9
1.4 PURPOSE AND SIGNIFICANCE OF THE PRESENT STUDY ................................................................................................ 11
2. MATERIALS & METHODS ................................................................................................................................... 13
2.1 MODEL OVERVIEW ................................................................................................................................................... 13
2.2 MODEL STRUCTURE .................................................................................................................................................. 13
2.3 DATA SOURCES ......................................................................................................................................................... 15
2.4 AEROSOL TRANSMISSION MODELING ......................................................................................................................... 16
2.5 CLOSE CONTACT DROPLET TRANSMISSION MODELING ............................................................................................... 18
2.6 FOMITE-MEDIATED TRANSMISSION MODELING .......................................................................................................... 18
2.7 MODELED SCENARIOS ............................................................................................................................................... 19
2.7.1 Transportation Scenario ................................................................................................................................. 20
2.7.2 Residential Scenario ....................................................................................................................................... 21
2.7.3 Outdoor Field Harvesting Scenario ................................................................................................................ 22
2.7.4 Indoor Packing Facility Scenario ................................................................................................................... 23
2.8 RISK ASSESSMENT .................................................................................................................................................... 23
2.8.1 Sensitivity Analysis .......................................................................................................................................... 25
2.9 INTERVENTION IMPACT TESTING ............................................................................................................................... 26
3. MODELING RESULTS ............................................................................................................................................ 28
3.1 RISK OF INFECTION IN TRANSPORTATION MEDIUM ..................................................................................................... 28
3.2 RISK OF INFECTION IN RESIDENTIAL AREA ................................................................................................................. 29
3.3 RISK OF INFECTION IN OUTDOOR HARVESTING FIELD ................................................................................................. 29
3.4 RISK OF INFECTION IN INDOOR PACKAGING FACILITY ................................................................................................ 30
3.5 EFFECTS OF FACE MASK ON REDUCING INFECTION RISK ............................................................................................. 31
3.6 EFFECTS OF HAND HYGIENE INTERVENTIONS ON REDUCING INFECTION RISK .............................................................. 31
3.7 EFFECTS OF SURFACE DISINFECTION INTERVENTIONS ON REDUCING INFECTION RISK ................................................. 32
3.8 EFFECTS OF INCREASED AIR EXCHANGE RATES ON REDUCING INFECTION RISK .......................................................... 33
3.9.1 DAILY CUMULATIVE RISK BASED ON CONTACT LOCATION ...................................................................................... 34
3.9.2 DAILY CUMULATIVE RISK BASED ON INTERVENTION PACKAGE IMPLEMENTATION .................................................. 35
3.9.3 SENSITIVITY ANALYSES ......................................................................................................................................... 36
4. DISCUSSION ............................................................................................................................................................. 37
4.1 RISK OF SARS-COV-2 INFECTION IS INFLUENCED BY LOCATION OF EFFECTIVE CONTACT ............................................ 37
4.2 RISK OF SARS-COV-2 INFECTION IS DIFFERENTIALLY REDUCED BY INTERVENTION TYPE ............................................ 41
4.3 MODELING STRENGTHS, LIMITATIONS, & FUTURE DIRECTIONS .................................................................................. 46
4.4 CONCLUSIONS & PUBLIC HEALTH RECOMMENDATIONS ............................................................................................. 48
5. BIBLIOGRAPHY ...................................................................................................................................................... 50
6. TABLES & FIGURES ............................................................................................................................................... 66
TABLE 1A-C. MODEL PARAMETERS & DISTRIBUTIONS ..................................................................................................... 66
FIGURE 1. SARS-COV-2 QMRA SCHEMATIC ...................................................................................................................... 69
FIGURE 2. RISK OF SARS-COV-2 INFECTION ACROSS FOUR MODELED SCENARIOS ............................................................. 70
FIGURE 3. REDUCTION IN SARS-COV-2 INFECTION RISK ATTRIBUTED TO FACE MASK UTILIZATION ................................... 72
FIGURE 4. REDUCTION IN SARS-COV-2 INFECTION RISK ATTRIBUTED TO HAND HYGIENE INTERVENTIONS ........................ 74
FIGURE 5. REDUCTION IN SARS-COV-2 INFECTION RISK ATTRIBUTED TO SURFACE DISINFECTION FREQUENCY .................. 76
FIGURE 6. REDUCTION IN SARS-COV-2 INFECTION RISK ATTRIBUTED TO INCREASED AIR EXCHANGE RATES .................... 77
TABLE 3. CUMULATIVE RISK OF SARS-COV-2 INFECTION BASED ON LOCATION OF CONTACT ........................................... 79
TABLE 4A-B. CUMULATIVE RISK OF SARS-COV-2 INFECTION AFTER INTERVENTION PACKAGE IMPLEMENTATION ............. 80
7. SUPPLEMENTAL MATERIALS ........................................................................................................................... 82
SUPPLEMENTAL TABLE 1. AEROSOL TRANSPORTATION MODEL PARAMETERS FOR INDOOR PACKAGING FACILITY ............. 82
SUPPLEMENTAL FIGURE 1. SPEARMAN’S RHO CORRELATION COEFFICIENTS ..................................................................... 83
SUPPLEMENTAL TABLE 2. SENSITIVITY ANALYSIS RESULTS ............................................................................................. 84
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