Stores everywhere have implemented different types of safety measures to prevent the transmissions of COVID-19 among shoppers. Many use distance markers and “one-way” paths through the store, some offer special hours reserved for high-risk shoppers, and often, limits on the number of in-store customers are imposed. The combination and exact implementation of these measures vary between stores and regions. A better understanding of their effects on virus transmission could help to optimize COVID-19 prevention in retail environments.
Robert A. Shumsky, Dartmouth College, Hanover, NH, USA, and colleagues have investigated the rate of disease transmission in retail stores by combining simple models of customer traffic flow and disease transmission. The team focused on infection via respiratory droplets and aerosols, considered to be the most common pathways of COVID-19 transmission. To capture these two types of transmission, they used one model for direct transmission when two customers are close to each other, and another model for the potential aerosol transmission that occurs when a customer moves in the more distant “wake” of another customer. They considered, e.g., facility size, customer movement, the fraction of infectious customers, and aerosol diffusion to predict the overall rate of new infections in a store.
The researchers found that one-way movement can dramatically reduce direct droplet transmission from close contact. However, the impact of one-way aisles on aerosol transmission is limited. Customers are less likely to move close to each other, but they spend more time walking in the “wake” of the customer in front. According to the team, these effects cancel each other out. Overall, they found that the optimal customer throughput rate drops rapidly as the fraction of contagious people rises, which makes customer limits increasingly uneconomic.
- Retail store customer flow and COVID-19 transmission,
Robert A. Shumsky, Laurens Debo, Rebecca M. Lebeaux, Quang P. Nguyen, Anne G. Hoen,
Proc. Natl. Acad. Sci. USA 2021, 118, e2019225118.
https://doi.org/10.1073/pnas.2019225118
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