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Why are gatherings not recommended during the outbreak of COVID-19 ?

Text updated on 2020-06-23

Super-propagation events have mainly taken place at large gatherings where people are confined to indoors (choir, cruise ship, festival, rush-hour transit, prison, slaughterhouse, or school). Some outbreaks also started outdoors during festivals, sporting events, or demonstrations.

Large gatherings have a special feature:

Certain activities, especially singing, shouting, or playing sports, lead to a high emission of droplets and aerosols that can effectively transmit the SARS-CoV-2 coronavirus to people close by. The likelihood of contamination increases with the number of people together and the time spent together.

As a result, many super-propagation events, in which the virus was transmitted by a super-propagator to many people, took place at large gatherings usually, but not exclusively indoors.

If a large gathering is necessary, encourage exchanges outside, with respect for social distancing and the wearing of a mask or even a face shield!

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In Japan, many cases of contamination in epidemiological "outbreaks" or "clusters" took place in closed places: sports hall, restaurant boat, hospital, festivals where there were tents with minimal ventilation for eating.

Nishiura, H., Oshitani, H., Kobayashi, T., Saito, T., Sunagawa, T., Matsui, T., ... & Suzuki, M. (2020). Closed environments facilitate secondary transmission of coronavirus disease 2019 (COVID-19). medRxiv.

Article submitted on May 27th which takes stock of the superspreader events in the context of the spread of the epidemic of COVID-19 and identifies the key factors of a superspreader event.

Althouse, B. M., Wenger, E. A., Miller, J. C., Scarpino, S. V., Allard, A., Hébert-Dufresne, L., & Hu, H. (2020). Stochasticity and heterogeneity in the transmission dynamics of SARS-CoV-2. arXiv preprint arXiv:2005.13689.

The 60 members of a choir gathered in a room to sing for 2.5 hours on March 10, 2020 in Washington State, USA. They kept a safe distance, used hydro-alcoholic solutions, but did not put on masks. Three weeks later, 45 of them tested positive for COVID-19.

Los Angeles Times article of March 29, 2020.

The analysis of 318 cases where one person contaminated at least 2 other people in China (for a total of 1,245 COVID+ individuals) reveals that the majority of the contaminations took place in a closed space, mainly in the home and during transport, but also in restaurants, and that only one contamination took place following an open-air discussion with a person returning from Wuhan.

Qian, H., Miao, T., Li, L. I. U., Zheng, X., Luo, D., & Li, Y. (2020). Indoor transmission of SARS-CoV-2. medRxiv.

Analysis of the first epidemic outbreaks in the United Kingdom, France, and Spain.

Hodcroft, E. B. (2020). Preliminary case report on the SARS-CoV-2 cluster in the UK, France, and Spain.

Analysis of an outbreak showing that large family gatherings such as funerals and birthday parties can be events where transmission of the SARS-CoV-2 coronavirus is significant.

Ghinai, I., Woods, S., Ritger, K. A., McPherson, T. D., Black, S. R., Sparrow, L., ... & Arwady, M. A. (2020). Community transmission of SARS-CoV-2 at two family gatherings-Chicago, Illinois, February-March 2020.

This study shows that the higher the voice volume (amplitude), the higher the number of particles emitted during speech, ranging from 1 to 50 particles per second (0.06 to 3 particles per cm3) for low to high amplitudes, regardless of the language spoken (English, Spanish, Mandarin or Arabic). In addition, a small fraction of individuals behave as "super emitters", systematically releasing ten more particles than others.

Asadi, S., Wexler, A. S., Cappa, C. D., Barreda, S., Bouvier, N. M., & Ristenpart, W. D. (2019). Aerosol emission and superemission during human speech increase with voice loudness. Scientific reports, 9(1), 1-10.

Further reading

What is a superspreader event for COVID-19 ?

Why are superspreader events crucial to understanding the COVID-19 epidemic?

What is the purpose of social distancing?

What are the physical effects of confinement and social distancing?