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Practical Indicators for Risk of Airborne Transmission in Shared Indoor Environments and Their Application to COVID-19 Outbreaks

Peng, Z.; Rojas, A.L. Pineda; Kropff, E.; Bahnfleth, W.; Buonanno, G.; Dancer, S.J.; Kurnitski, J.; Li, Y.; Loomans, M.G.L.C.; Marr, L.C.; Morawska, L.; Nazaroff, W.; Noakes, C.; Querol, X.; Sekhar, C.; Tellier, R.; Greenhalgh, T.; Bourouiba, L.; Boerstra, A.; Tang, J.W.; Miller, S.L.; Jimenez, J.L.


Z. Peng

A.L. Pineda Rojas

E. Kropff

W. Bahnfleth

G. Buonanno

J. Kurnitski

Y. Li

M.G.L.C. Loomans

L.C. Marr

L. Morawska

W. Nazaroff

C. Noakes

X. Querol

C. Sekhar

R. Tellier

T. Greenhalgh

L. Bourouiba

A. Boerstra

J.W. Tang

S.L. Miller

J.L. Jimenez


Some infectious diseases, including COVID-19, can undergo airborne transmission. This may happen at close proximity, but as time indoors increases, infections can occur in shared room air despite distancing. We propose two indicators of infection risk for this situation, that is, relative risk parameter (Hr) and risk parameter (H). They combine the key factors that control airborne disease transmission indoors: virus-containing aerosol generation rate, breathing flow rate, masking and its quality, ventilation and aerosol-removal rates, number of occupants, and duration of exposure. COVID-19 outbreaks show a clear trend that is consistent with airborne infection and enable recommendations to minimize transmission risk. Transmission in typical prepandemic indoor spaces is highly sensitive to mitigation efforts. Previous outbreaks of measles, influenza, and tuberculosis were also assessed. Measles outbreaks occur at much lower risk parameter values than COVID-19, while tuberculosis outbreaks are observed at higher risk parameter values. Because both diseases are accepted as airborne, the fact that COVID-19 is less contagious than measles does not rule out airborne transmission. It is important that future outbreak reports include information on masking, ventilation and aerosol-removal rates, number of occupants, and duration of exposure, to investigate airborne transmission.

Journal Article Type Article
Acceptance Date Dec 13, 2021
Online Publication Date Jan 5, 2022
Publication Date Jan 18, 2022
Deposit Date Feb 11, 2022
Publicly Available Date Feb 11, 2022
Journal Environmental Science & Technology
Print ISSN 0013-936X
Electronic ISSN 1520-5851
Publisher American Chemical Society
Peer Reviewed Peer Reviewed
Volume 56
Issue 2
Pages 1125-1137
Keywords COVID-19, airborne transmission, outbreaks, indoor air, risk assessment, mitigation
Public URL


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