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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:

que les personnes sont souvent plus rapprochées que la distance préconisée (< 1-2 m),
there is a large number of people (group of more than 10 people),
that people are going to spend more than an hour or two together,
that people are easily susceptible to exchanging viral particles orally: by talking, singing, shouting, eating at the same table, or playing sports.

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, favour your exchanges outside, with respect for physical distance and the wearing of a mask and/or even a visor!

Sources

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.

Study of 961 patients with COVID-19 in Hong Kong between December 2019 and April 2020 and the cause of their contamination. Non-masked" leisure activities, such as eating and drinking in restaurants and bars, singing in a karaoke bar, or playing sports in a gym, led to significantly more cases of contamination than "masked" work environments.

Cheng, V. C., Wong, S. C., Chuang, V. W., So, S. Y., Chen, J. H., Sridhar, S., ... & Yuen, K. Y. (2020). The role of community-wide wearing of face mask for control of coronavirus disease 2019 (COVID-19) epidemic due to SARS-CoV-2. Journal of Infection.

Two groups of 8 people went to perform karaoke in Guangkhu, China in January 2020, without masks. In one group there was a presymptomatic person and in the other one an asymptomatic person. The people sitting next to them became infected.

Gu, Y., Lu, J., Su, W., Liu, Y., Xie, C., & Yuan, J. (2020). Transmission of SARS-CoV-2 in the Karaoke Room: An Outbreak of COVID-19 in Guangzhou, China, 2020. Journal of epidemiology and global health.