Modelling airborne transmission of SARS-CoV-2 using CARA: risk assessment for enclosed spaces

Abstract

The COVID-19 pandemic has highlighted the need for a proper risk assessment of respiratory pathogens in indoor settings. This paper documents the COVID Airborne Risk Assessment methodology, to assess the potential exposure of airborne SARS-CoV-2 viruses, with an emphasis on virological and immunological factors in the quantification of the risk. The model results from a multidisciplinary approach linking physical, mechanical and biological domains, enabling decision makers or facility managers to assess their indoor setting. The model was benchmarked against clinical data, as well as two real-life outbreaks, showing good agreement. A probability of infection is computed in several everyday-life settings and with various mitigation measures. The importance of super-emitters in airborne transmission is confirmed: 20% of infected hosts can emit approximately two orders of magnitude more viral-containing particles. The use of masks provides a fivefold reduction in viral emissions. Natural ventilation strategies are very effective to decrease the concentration of virions, although periodic venting strategies are not ideal in certain settings. Although vaccination is an effective measure against hospitalization, their effectiveness against transmission is not optimal, hence non-pharmaceutical interventions (ventilation, masks) should be actively supported. We also propose a critical threshold to define an acceptable risk level.

Overview of the Role of Spatial Factors in Indoor SARS-CoV-2 Transmission: A Space-Based Framework for Assessing the Multi-Route Infection Risk

“…Furthermore, different Spanish research groups have developed a Aireamos [ 144 ] platform employing various types of ventilation strategies by analyzing CO 2 levels to assess and control the indoor COVID-19 infection risk. In addition, Henriques et al [ 145 ] have established a COVID-19 airborne risk-assessment methodology, which proved that single-sided, naturally ventilated classrooms with windows slightly open in winter can result in a 2.2-fold reduction in the infection dose. In addition to ventilation efficiency, the location of the infected individual also needs to be emphasized.…”

A review on indoor airborne transmission of COVID-19– modelling and mitigation approaches

“…This methodology has been followed by other studies as well [ [31] , [32] , [33] , [34] ]. However, the assumptions adopted by this method are not rigorous enough in view of virology because the emitted viral-laden particles can be affected by factors such as the host immune responses and the physical properties of the oropharyngeal fluids [ 35 ] and, in addition, the aerosol viral loads can be much lower than the viral swab load [ 36 ]. With this regard, a more interdisciplinary effort is needed to identify the viral load for indoor studies.…”

Informing Building Strategies to Reduce Infectious Aerosol Transmission Risk by Integrating DNA Aerosol Tracers with Quantitative Microbial Risk Assessment

“…We propose a method for combining airborne pathogen transmission risk modeling and physical tracer measurements for modeling the risk reduction that results from infectious aerosol exposure mitigation measures. This is accomplished by integrating quantitative microbial risk assessment (QMRA) − with aerosol concentrations of synthetic DNA tracers collected in buildings. − …”

“…Schijven et al developed a QMRA model to estimate SARS-CoV-2 aerosol transmission risk, described here as a “bulk aerosol” QMRA model, as once aerosolized pathogen numbers are estimated the particle size distribution is not further considered. Henriques et al developed a particle size-resolved QMRA model for SARS-CoV-2, increasing the accuracy of the inhalation dose by modeling particle size-dependent emission, transport, and removal. , Due to the complexity and computational intensity of the particle size-resolved approach, and due to the use of bulk aerosol collection methods with aerosol tracers, the bulk aerosol QMRA model approach is adopted here. We iterate on the model of Schijven et al, incorporating parametrizations for the survival of pathogens during aerosolization, biological decay of aerosolized pathogens, multiple-occupant scenarios, and interventions such as adding ventilation and masking.…”