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Miller, Shelly l., Nazaroff, William W. et al. 2020. “Transmission of SARS‐CoV‐2 by inhalation of respiratory aerosol in the Skagit Valley Chorale superspreading event.” International Journal of Indoor Environment and Health, 2020;00:1–10.

During the 2020 COVID‐19 pandemic, an outbreak occurred following attendance of a symptomatic index case at a weekly rehearsal on 10 March of the Skagit Valley Chorale (SVC). After that rehearsal, 53 members of the SVC among 61 in attendance were confirmed or strongly suspected to have contracted COVID‐19 and two died. Transmission by the aerosol route is likely; it appears unlikely that either fomite or ballistic droplet transmission could explain a substantial fraction of the cases. It is vital to identify features of cases such as this to better understand the factors that promote superspreading events. Based on a conditional assumption that transmission during this outbreak was dominated by inhalation of respiratory aerosol generated by one index case, we use the available evidence to infer the emission rate of aerosol infectious quanta. We explore how the risk of infection would vary with several influential factors: ventilation rate, duration of event, and deposition onto surfaces. The results indicate a best‐estimate emission rate of 970 ± 390 quanta/h. Infection risk would be reduced by a factor of two by increasing the aerosol loss rate to 5 h−1 and shortening the event duration from 2.5 to 1 h.

Practical Implications:

  • During respiratory disease pandemics, group singing indoors should be carefully managed as singing can generate large amounts of aerosolized virus if any of the singers is infected.
  • Ventilation requirements for spaces that are used for singing (eg, buildings for religious services and rehearsal/performance) should be reconsidered in light of the potential for aerosol transmission of infectious diseases.
  • Systems that combine the functions heating and ventilation (or cooling and ventilation) should be accompanied with a disclaimer saying “do not shut this system off when people are using the room; turning off the system will also shut down outdoor air supply, which can lead to the spread of airborne infections.”

https://onlinelibrary.wiley.com/doi/10.1111/ina.12751

PDF: https://onlinelibrary.wiley.com/doi/epdf/10.1111/ina.12751

NOTES:
all authors:
Shelly L. Miller William W Nazaroff Jose L. Jimenez Atze Boerstra Giorgio Buonanno Stephanie J. Dancer Jarek Kurnitski Linsey C. Marr Lidia Morawska Catherine Noakes

Official journal of the International Society of Indoor Air Quality and Climate

Publication History
Version of Record online:
13 October 2020
Accepted manuscript online:
26 September 2020
Manuscript accepted:
15 September 2020
Manuscript revised:
26 August 2020
Manuscript received:
16 June 2020

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