Controlling risk of SARS-CoV-2 infection in essential workers of enclosed food manufacturing facilities

Abstract

The SARS-CoV-2 global pandemic poses significant health risks to workers who are essential to maintaining the food supply chain. Using a quantitative risk assessment model, this study characterized the impact of risk reduction strategies for controlling SARS-CoV-2 transmission (droplet, aerosol, fomite-mediated) among front-line workers in a representative indoor fresh fruit and vegetable manufacturing facility. We simulated: 1) individual and cumulative SARS-CoV-2 infection risks from close contact (droplet and aerosols at 1-3 m), aerosol, and fomite-mediated exposures to a susceptible worker following exposure to an infected worker during an 8 h-shift; and 2) the relative reduction in SARS-CoV-2 infection risk attributed to infection control interventions (physical distancing, mask use, ventilation, surface disinfection, hand hygiene, vaccination). Without mitigation measures, the SARS-CoV-2 infection risk was largest for close contact (droplet and aerosol) at 1 m (0.96, 5th - 95th percentile: 0.67-1.0). In comparison, risk associated with fomite (0.26, 5th - 95th percentile: 0.10-0.56) or aerosol exposure alone (0.05, 5th - 95th percentile: 0.01-0.13) at 1 m distance was substantially lower (73-95%). At 1 m, droplet transmission predominated over aerosol and fomite-mediated transmission, however, this changed by 3 m, with aerosols comprising the majority of the exposure dose. Increasing physical distancing reduced risk by 84% (1-2 m) and 91% (1-3 m). Universal mask use reduced infection risk by 52-88%, depending on mask type. Increasing ventilation (from 0.1 to 2-8 air changes/hour) resulted in risk reductions of 14-54% (1 m) and 55-85% (2 m). Combining these strategies, together with handwashing and surface disinfection, resulted in <1% infection risk. Partial or full vaccination of the susceptible worker resulted in risk reductions of 73-92% (1 m risk range: 0.08-0.26). However, vaccination paired with other interventions (ACH 2, mask use, or distancing) was necessary to achieve infection risks <1%. Current industry SARS-CoV-2 risk reduction strategies, particularly when bundled, provide significant protection to essential food workers.

Keywords: Aerosol; And fomite-mediated transmission; COVID-19; Droplet; Quantitative microbial risk assessment; Vaccination.

Fig. 1

A-B. SARS-CoV-2 QMRA schematic for respiratory event (coughing versus breathing) and infection risk through aerosol, close contact (1–3 m, droplet and aerosol), and fomite-mediated transmission assuming no risk mitigation interventions. A. This conceptual model depicts the three transmission pathways (close contact [droplet and aerosol], aerosol, and fomite-mediated) within a representative food manufacturing facility, initiating with a single infected worker either coughing (symptomatic) or breathing (asymptomatic) to generate virus-containing respiratory droplets and aerosols. Droplets fall rapidly due to gravitational forces and were categorized by size and distance traveled from source based on empirical experiments and modeling studies (Bourouiba et al., 2014; Wei & Li, 2015): <1 m (50–750 μm), 1–2 m (50–100 μm), and 2–3 m (50–60 μm). Aerosols were defined as <50 μm in diameter with the ability to become aerosolized and remain suspended in the air throughout the entire facility space. B. Infection risk from combined transmission events (aerosol, droplet, fomite-mediated) in association with exposure to an infected worker (coughing) over a period of 1–8 h and as a function of distance. Results are presented as the median risk values with 5th and 95th percentile bars.

Fig. 2

Impact of increasing air exchange on combined infection risk reduction following an 8 h-exposure to an infected worker (coughing) at various distances. For reference, air changes per hour (ACH) of 2–6 are representative of typical indoor food manufacturing facilities based on survey results. Included percentages represent the percent reduction in SARS-CoV-2 infection risk relative to no air exchange (baseline ACH = 0.1) for combined risk at the four distances (1 m, 2 m, 3 m, and >3 m) modeled. Results are presented as the median risk values with 5th and 95th percentile bars.

Fig. 3

Impact of vaccination alone or in combination with interventions (universal cloth, surgical, or double mask use, ventilation [2 ACH]) on infection risk following 8 h cumulative exposure to an infected worker at 1 m distancing. No immunity reference group represents infection risk with baseline ACH = 0.1 in the absence of vaccination or any interventions. For the partial and full immunity scenarios, both the infected and susceptible workers were assumed to be vaccinated with at least one of two doses. Under these scenarios, the infected worker represented a rare breakthrough infection event in which vaccination led to reduced virus shedding for the infected worker (2.8-fold reduction) (Levine-Tiefenbrun et al., 2021). For the partial immunity scenario, the vaccinated susceptible worker had a 52–74% reduction in infection risk representative of a single dose of the two-dose mRNA vaccine series, or reduced vaccine efficacy against SARS-CoV-2 variants (FDA, 2021a, 2021b, Polack et al., 2020). For the full immunity scenario, the vaccinated susceptible worker had a 77–99% reduction in infection risk representative of ≥14 days after the second dose derived from vaccine effectiveness data for the Johnson & Johnson/Janssen, Pfizer-BioNTech, Moderna, and AstraZeneca vaccines (Corchado-Garcia et al., 2021; Swift et al., 2021). Results are presented as the median risk values with 5th and 95th percentile bars.