Mass Flow Analysis of SARS-CoV-2 for quantified COVID-19 Risk Analysis

TL;DR

This study models and quantifies SARS-CoV-2 transmission routes using a material metabolism approach, identifying high-risk scenarios like closed spaces and long-duration close contacts for targeted COVID-19 risk mitigation.

Contribution

It applies industrial ecology mass flow analysis to SARS-CoV-2 transmission, providing a quantitative framework for assessing exposure risks across different scenarios.

Findings

Closed rooms pose the highest exposure risks even with good ventilation.

Close person-to-person contact has significantly lower but notable risks.

Open spaces generally have an order of magnitude lower exposure risks.

Abstract

How may exposure risks to SARS-CoV-2 be assessed quantitatively? The material metabolism approach of Industrial Ecology can be applied to the mass flows of these virions by their numbers, as a key step in the analysis of the current pandemic. Several transmission routes of SARS-2 from emission by a person to exposure of another person have been modelled and quantified. Start is a COVID-19 illness progression model specifying rising emissions by an infected person: the human virion factory. The first route covers closed spaces, with an emission, concentration, and decay model quantifying exposure. A next set of routes covers person-to-person contacts mostly in open spaces, modelling the spatial distribution of exhales towards inhalation. These models also cover incidental exposures, like coughs and sneezes, and exposure through objects. Routes through animal contacts, excrements, and food, have not been quantified. Potential exposures differ by six orders of magnitude. Closed rooms, even with reasonably (VR 2) to good (VR 5) ventilation, constitute the major exposure risks. Close person-to-person contacts of longer duration create two orders of magnitude lower exposure risks. Open spaces may create risks an order of magnitude lower again. Burst of larger droplets may cause a common cold but not viral pneumonia as the virions in such droplets cannot reach the alveoli. Fomites have not shown viable viruses in hospitals, let alone infections. Infection by animals might be possible, as by cats and ferrets kept as pets. These results indicate priority domains for individual and collective measures. The wide divergence in outcomes indicates robustness to most modelling and data improvements, hardly leading to major changes in relative exposure potentials. However, models and data can substantially be improved.