The transmission of Covid-19 during a bus trip as part of a religious event in China last January has been analyzed. The thesis of aerosol contamination is thus confirmed.
- A Chinese study looks back on the case of the formation of a cluster during a religious event in January 2020.
- The researchers note that 1/3 of the passengers on a bus were infected while the other participants who did not travel on this bus were not or very little.
- The study suspects transmission of the virus by aerosol because the bus was ventilated by internal air recycling.
What if Covid-19 was not transmitted only by large droplets but also by aerosol, i.e. not simple breathing? This is the thesis defended a new study published this Tuesday, September 1 in the American journal JAMA internal medicine. In this article, Chinese scientists trace the case of contamination of a bus chartering travelers where a third of the passengers apparently contracted the virus on this occasion because of a single person.
Scientists have analyzed in detail the case of this contamination taking place in the region of Zhejiang (China) located south of Shanghai. On January 19, 2020, at the start of the pandemic, 128 people in two buses traveled 50 minutes one way and 50 minutes back to the city of Ningbo. They join a religious event in which 172 other individuals participate. Travelers who made this 1h40 journey are mostly women (88%) and have an average age of 58 years. Nobody wore a mask and the air of the two buses was recycled internally, therefore without renewal of the air inside the cabin. After this trip, experts from the Chinese Centers for Disease Control find that 24 of the 68 people on the No. 2 bus (35%) were positive for Covid-19, compared to 7 of 172 (4%) for the other people. of the gathering and no case was identified in bus n°1. Because of this, the researchers assume that the cluster formed inside bus n°2. By questioning each traveler, they note that only one sexagenarian has been in contact with the inhabitants of Wuhan. They believe that she must have been the source of the contamination.
Mysterious spread
However, when they meet 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 sitting in the middle of the bus, but cases positive for Covid-19 were found at the front and at the back of the bus, at a distance greater than 2m where the postilions could not reach them. In addition, the sexagenarian was asymptomatic, either she did not cough or sneeze.
Even more disturbing, 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 brought the virus into contact with other passengers via the mixing of the air. Researchers are alerting public authorities to consider 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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