Quantifying Proximity, Confinement, and Interventions in Disease Outbreaks: A Decision Support Framework for Air-Transported Pathogens

Abstract

The inability to communicate how infectious diseases are transmitted in human environments has triggered avoidance of interactions during the COVID-19 pandemic. We define a metric, Effective ReBreathed Volume (ERBV), that encapsulates how infectious pathogens, including SARS-CoV-2, transport in air. ERBV separates environmental transport from other factors in the chain of infection, allowing quantitative comparisons among situations. Particle size affects transport, removal onto surfaces, and elimination by mitigation measures, so ERBV is presented for a range of exhaled particle diameters: 1, 10, and 100 μm. Pathogen transport depends on both proximity and confinement. If interpersonal distancing of 2 m is maintained, then confinement, not proximity, dominates rebreathing after 10–15 min in enclosed spaces for all but 100 μm particles. We analyze strategies to reduce this confinement effect. Ventilation and filtration reduce person-to-person transport of 1 μm particles (ERBV1) by 13–85% in residential and office situations. Deposition to surfaces competes with intentional removal for 10 and 100 μm particles, so the same interventions reduce ERBV10 by only 3–50%, and ERBV100 is unaffected. Prior knowledge of size-dependent ERBV would help identify transmission modes and effective interventions. This framework supports mitigation decisions in emerging situations, even before other infectious parameters are known.

Fates and spatial variations of accumulation mode particles in a multi-zone indoor environment during the HOMEChem campaign

“…These discrepancies are particularly relevant when considering the effectiveness of ventilation in controlling particle lifetime -Bond et al (2020) suggest that these discrepancies in predicted indoor deposition rate may be substantial enough to impact recommendations for different mitigation techniques for reducing exhaled respiratory aerosol exposure. 50 Coagulation is a second order process, dependent on concentration and is therefore important in areas of high concentrations, however, initial analysis of the size distribution over the course of typical cooking events did not indicate evidence of coagulation within the measured size range (Fig. S18 †).…”

Risk assessment of airborne COVID-19 exposure in social settings

“…Over the course of this pandemic, various authors have noted the need for a more intuitive way of comparing transmission risk and mitigation measures and communicating the results to a less technical audience, including via a decision support framework based on effective rebreathed volume (ERBV). 39 In this work, we propose the use of a three-tiered risk assessment system to evaluate the potential for COVID-19 transmission across different real-world scenarios and locations. Threshold values are chosen based on the current literature for converting high-fidelity but less interpretable results from both numerical CFD studies and experimental surrogate aerosol studies into a three-tiered risk assessment scale for direct qualitative comparison.…”

“…Importantly, many authors have noted the need for a more intuitive way of comparing transmission risk and communicating results to stakeholders, including policy-makers, in a more interpretable and actionable form. 39,40 Hence, we further propose a 3-tiered risk assessment scheme based on results from CFD and surrogate aerosol experiments. This also builds on prior proposals for a more nuanced implementation of risk mitigation measures such as physical distances.…”

End-to-end SARS-CoV-2 transmission risks in sport: Current evidence and practical recommendations

“…The closer the proximity between individuals and the longer the duration of the close proximity interactions, the greater the transmission risk of SARS-CoV-2, even when outdoors. [7,93] Some outdoor sporting activities may create indoor-like environmental characteristics (e.g. low ventilation, poor air flow), and therefore may remain high risk for transmission.…”