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On board a diamond princess, a case study in the field of aerosol transfer



“They still surprise us,” Dr. said. Conly. “I find this document interesting, but it must have been credible in my mind for a long time.”

George Rutherford, a professor of epidemiology at the University of California, San Francisco, was equally skeptical. He said that outside the hospital environment, “big drops in my mind are responsible for the vast majority of cases. Aerosol transmission – if you actually ride it, it creates a lot of discrepancies. Are there situations where this could occur? Yes, maybe, but it’s a small amount. “

Tang and other scientists strongly disagree. “If I talk to an infectious person for 1

5 or 20 minutes and inhale some of their air,” Dr. said. Tang, “Isn’t this a much easier way to explain the transmission, how to touch the infected surface and touch your eyes?” When you talk about a fireplace, for example in a restaurant, this seems like a torturous way to explain the transmission. “

In a new analysis, a team led by indoor air researcher Parham Azimi at the TH Chan Harvard School of Public Health studied the focus of diamonds, where physical spaces and infections were well documented. More than 20,000 simulations of how the virus could spread throughout the ship were performed. Each simulation made a number of assumptions about factors such as patterns of social interaction – how much time people spent in the cabin, on board or in the cafe, on average – and the amount of time the virus can live on surfaces. Each also took into account the different contributions of smaller floating droplets, which are generally defined as 10 microns or less; and larger drops that fall faster and infect surfaces or other persons, for example by landing on the eyes, mouth or nose.

About 130 of these simulations reproduced to some extent what actually happened to the diamond princess as the focus expanded. By analyzing these most realistic scenarios, the research team calculated the most likely contributions of each transmission pathway. The researchers concluded that smaller droplets predominated and accounted for about 60 percent of all new infections, in close proximity, a few meters from the infectious person, and at greater distances.

“A lot of people said there was an air transmission, but no one had numbers,” said Dr. Azimi. “What is the benefit of these little droplets – is it 5 percent or 90 percent?” In this document, we present the first real estimates of what the number could be, at least for this cruise ship. “

The logic of this transfer is clear, experts said. When someone speaks, it emits a cloud of droplets, the vast majority of which are small enough to remain in the air for a few minutes or longer. By inhalation, this cloud of small droplets is more likely to reach the mucus membrane than the larger ones, which rise ballistically.


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