In January, at the very start of what would become the Covid-19 pandemic, an infected and asymptomatic passenger contaminated a third of his poorly ventilated coach during a journey of less than an hour, new clue that the coronavirus is very likely transmissible by air.

A textbook case of airborne transmission of the coronavirus: a Chinese bus

The thesis of the transmission of the virus by the air that everyone exhales and inhales, rather than by the only large droplets expelled by sneezing and coughing, was initially neglected by the health authorities of the world, before a turnaround operated this summer in the face under pressure from many respiratory virus experts and an accumulation of studies on the presence of viral particles in airborne microdroplets ejected by mere speech.

In an article published Tuesday by the American medical journal Jama Internal Medicine, experts from the Chinese Centers for Disease Control describe interviewing and testing passengers who were taken in two buses to a Buddhist event in Ningbo city on January 19. , during a 50-minute journey (with return in the same two coaches). No one wore a mask.

A person in her sixties, without symptoms, was most likely the index case, as she had previously had contact with people in Wuhan, where the epidemic started. She was seated on the right side in a row in the middle of coach number 2, between two other passengers.

A total of 23 other passengers on this bus were infected, out of 68 people. Conversely, no infection was found in bus number one, which is identical.

What is notable is that the circle of infections was much larger than the few rows around the 60-year-old, with infected people in the front and back of the bus: if the virus was only transmitted by large droplets, the circle would have been smaller since they generally fall within a perimeter of one or two meters. In addition, the index patient had no symptoms at the time of the trips, so he was not coughing.

The bus’s air conditioning system recirculated the air inside the passenger compartment and did not renew it, which arguably helped spread the virus throughout the bus, the authors conclude.

This investigation suggests that, in closed environments where air is recirculated, SARS-CoV-2 is a highly transmissible pathogen“, they write.

Their study, meticulous and which includes a plan of the bus with the position of each contaminated person, is added to others going in the same direction, in particular the case of multiple contaminations between tables in a restaurant in Canton, again no doubt. allowed by a ventilation system that does not renew the indoor air.

Created Sep 02, 2020