THE ESSENTIAL
- A Chinese study looks at the case of the formation of a cluster during a religious event in January 2020.
- The researchers note that 1/3 of the passengers of a bus were contaminated while the other participants who did not travel in this bus were not or very little.
- The study suspects transmission of the virus by aerosol because the bus was ventilated by internal recycling of the air.
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What if Covid-19 was not transmitted only by large droplets but also by aerosol, i.e. not simple breathing? This is the thesis that defends a new study published this Tuesday, September 1 in the American journal JAMA internal medicine. In this article, Chinese scientists retrace the case of contamination of a bus chartering travelers where a third of the passengers apparently contracted the virus on this occasion from a single person.
Scientists have analyzed in detail the case of this contamination taking place in the Zhejiang region (China) located south of Shanghai. On January 19, 2020, at the start of the pandemic, 128 people divided into two buses made a 50-minute trip then 50 minutes return to reach the city of Ningbo. They join a worship event in which 172 other individuals participate. The majority of travelers making this 1h40 trip are women (88%) and have an average age of 58 years. No one was wearing a mask and the air from the two buses was recycled internally, so there was no renewal of the air inside the cabin. After this trip, experts from the Chinese Centers for Disease Control found that 24 people out of the 68 of the No. 2 bus (35%) were positive for Covid-19, against 7 out of 172 (4%) for other people. of the rally and no case was recorded in bus n ° 1. Because of this, the researchers assume that the cluster formed inside the # 2 bus. By interviewing each traveler, they note that only one sixty-year-old has been in contact with residents of Wuhan. They believe that it must have been the source of the contamination.
Mysterious spread
However, when they pass the contaminated people with their location inside the bus, they discover with surprise that these people are not necessarily near the suspect sexagenarian. The latter was seated in the middle of the bus, but positive cases for Covid-19 were found at the front and at the back of the bus, i.e. at a distance of more than 2m where the postilions could not reach them. In addition, the sexagenarian was asymptomatic, either coughing or sneezing.
More troubling still, they found that the people closest to this woman were not the most infected. The researchers then assume that the virus was transmitted by aerosol and would have put the virus in contact with other passengers via the air mixing. The researchers alert the public authorities to take into consideration the aerosol transmission of the virus. One more argument for the generalized wearing of masks even if this mode of transmission is not unanimous among researchers.
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