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 enclosed food manufacturing facility. We simulated: 1) individual and cumulative SARS-CoV-2 infection risks from close contact (droplet and aerosols at 1-3m), aerosol, and fomite-mediated exposures to a susceptible worker following exposure to an infected worker during an 8h-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). Without mitigation measures, the SARS-CoV-2 infection risk was largest for close contact (droplet and aerosol) at 1m (0.96, 95%CI: 0.67-1.0). In comparison, risk associated with fomite (0.26, 95%CI: 0.10-0.56) or aerosol exposure alone (0.05, 95%CI: 0.01-0.13) at 1m distance was substantially lower (73-95%). At 1m, droplet transmission predominated over aerosol and fomite-mediated transmission, however, this changed by 3m, with aerosols comprising the majority of the exposure dose. Increasing physical distancing reduced risk by 84% (1 to 2m) and 91% (1 to 3m). 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% (1m) and 55-85% (2m). Combining these strategies, together with handwashing and surface disinfection, resulted in <1% infection risk. Current industry SARS-CoV-2 risk reduction strategies, particularly when bundled, provide significant protection to essential food workers.

Significance statement: Using mathematical modeling, we find that workers in enclosed food manufacturing facilities are at higher risk of SARS-CoV-2 infection from close contact transmission (exposure to large droplets and small aerosol particles) than fomite transmission. Thus, strategies protecting workers should prioritize close contact transmission pathways, such as physical distancing, universal mask use, and room air changes, with surface disinfection (reducing fomite transmission) and handwashing of secondary importance. Our work supports current international (EU-OSHA), domestic (FDA, OSHA), and food industry-standard guidance for managing COVID-19 transmission in essential workers in the food manufacturing sector. Although our model was designed for an indoor food manufacturing setting, it can be readily adapted to other indoor environments and infectious respiratory pathogens.

Figure 1.

A-B. SARS-CoV-2 QMRA schematic for respiratory event (coughing versus breathing) and infection risk through aerosol, close contact (1–3m, 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 (75, 110): <1m (50–750 μm), 1–2m (50–100 μm), and 2–3m (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.

Figure 2.

Impact of increasing air exchange on combined infection risk reduction following an 8h-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 (1m, 2m, 3m, and >3m) modeled.