This is undoubtedly the key point of the scientific study presented this month by Professor Yugou Li, of the University of Hong Kong on the occasion of a European congress on the Covid-19 epidemic: a diagram cross-section of a building in which we see the bathrooms and toilets of several apartments, stacked on top of each other and connected by a network of pipes. By way of explanation of this drawing, which reproduces a typical dwelling in a district of Hong Kong, a message warns: in each column of apartments, an ascending “chimney effect” can lead to the infection of the inhabitants located on the floors. superiors.
We had almost forgotten it by dint of insisting on barrier gestures or the contagiousness of variants, but the architecture of buildings also counts in the circulation of the epidemic. When you are infected and you brush your teeth or use the toilet, the virus begins to circulate in the drainpipes. It can even, in some cases, contaminate our neighbours. This type of vertical cluster is not new: scientists observed the phenomenon in 2009, during the H1N1 flu epidemic in Hong Kong. A decade later, the configuration of dwellings again plays its role in the spread of a virus.
“Traditional protective measures such as social distancing or staying home during acute phases of the outbreak may not be enough to stop the transmission of Covid-19 in densely populated high-rise buildings,” comments Professor Yugou Li. The warning does not only apply to Hong Kong but to all megalopolises. And it is based on a growing number of scientific studies.
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In The Annals of Internal Medicine, in September 2020, the researcher already detailed the appearance of a vertical cluster in a high-rise building located in Guangzhou, China. It was then nine cases grouped in three families. The first came from a recent trip to Wuhan, China. The other two, on the other hand, had no travel history and late onset of symptoms. At the time, no evidence of transmission via the elevator or other common area had been found. In contrast, the families lived in three apartments aligned vertically and connected by exhaust ducts.
Studies with consistent results
In 2021, scientists are looking into the contamination that occurred in four traditional “Tong Lau” houses typical of disadvantaged neighborhoods in Hong Kong. But this time, they are using gas to replicate the possible circulation of the virus. Closing? The outbreak was likely due to multiple routes of transmission, including drainpipes. A situation aggravated by poor ventilation in the apartments.
The latest study published in February 2022 also uses gas. “Its concentration coincides with the observed distribution of Covid cases from the apartments. Furthermore, sequencing and phylogenetic analyzes reveal a point-like and common source of contamination. CoV-2.”, emphasizes Professor Li.
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Of course, the most dangerous clusters appear when several unprotected people are concentrated in the same place. However, there are undoubtedly some lessons to be learned from the study of contamination in buildings. “We could, for example, use a handkerchief to avoid spitting in the sink,” says the professor. Certain pipelines, with multiple branches, could be simplified. But the most important lesson is undoubtedly addressed to the leaders: wanting to perfectly control the virus seems illusory.
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