Abstract
The COVID-19 pandemic has led to many countries oscillating between various states of lock-down as they seek to balance keeping the economy and essential services running and minimizing the risk of further transmission. Decisions are made about which activities to keep open across a range of social settings and venues guided only by ad hoc heuristics regarding social distancing and personal hygiene. Hence, we propose the dual use of computational fluid dynamic simulations and surrogate aerosol measurements for location-specific assessment of risk of infection across different real-world settings. We propose a 3-tiered risk assessment scheme to facilitate classification of scenarios into risk levels based on simulations and experiments. Threshold values of <54 and >840 viral copies and <5% and >40% of original aerosol concentration are chosen to stratify low, medium, and high risk. This can help prioritize allowable activities and guide implementation of phased lockdowns or re-opening. Using a public bus in Singapore as a case study, we evaluate the relative risk of infection across scenarios such as different activities and passenger positions and demonstrate the effectiveness of our risk assessment methodology as a simple and easily interpretable framework. For example, this study revealed that the bus's air-conditioning greatly influences dispersion and increases the risk of certain seats and that talking can result in similar relative risk to coughing for passengers around an infected person. Both numerical and experimental approaches show similar relative risk levels with a Spearman's correlation coefficient of 0.74 despite differing observables, demonstrating applicability of this risk assessment methodology to other scenarios.
Highlights
IntroductionCOVID-19 has spread worldwide with great speed and intensity causing much loss of life and economic damage
Over the past year, COVID-19 has spread worldwide with great speed and intensity causing much loss of life and economic damage
Assessment of relative risk due to different emitting activities. In such double-decker buses, passengers are likely to choose to sit in one of the two rows of seats facing forwards within the bus. This particular scenario is chosen as a case study for assessing the relative risk to others around a potentially infected passenger when the individual is talking for 5 min or coughing without a mask, or with a poorly worn mask
Summary
COVID-19 has spread worldwide with great speed and intensity causing much loss of life and economic damage. To mitigate the spread of COVID-19, experts have advocated three main interventions This includes the use of personal protective equipment (PPE), such as masks, face coverings, or face shields, active disinfection of shared places, and minimization of physical interaction via physical distancing guidelines and reduction of large-scale events, such as concerts, conferences, and sporting events.[1,2,3,4] Along those lines, there has been much work on developing more sophisticated PPE and refining the guidance on PPE efficacy.[5,6,7]. There is a need to re-allow some activities, even if many may end up in close physical proximity.[8,9] While some general guidelines for risk mitigation exist, including from the World Health Organization, additional science-based analysis of specific scenarios can be helpful for both risk assessment and subsequent customization
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