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Aboard the Diamond Princess, a Case Study in Aerosol Transmission

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“We are getting surprises all the time,” said Conly. “I find this article interesting, but there is still a long way to go to get a line of credibility.”

Dr. George Rutherford, 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 really use it, it creates a lot of dissonance. Are there situations in which this can occur? Yes, perhaps, but it is a small amount.

Dr. Tang and other scientists strongly disagree. “If I’m talking to an infectious person for 15 or 20 minutes and inhaling some air,” said Tang, “isn’t that a much simpler way of explaining transmission than touching an infected surface and touching your eyes? When you’re speaking of an outbreak, as in a restaurant, the latter seems to be a torturous way to explain the transmission. ”

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Updated July 27, 2020

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    • It could be a good idea, because mortgage rates have never been lower. Refinancing requests have taken mortgage requests to some of the highest levels since 2008, so be prepared to get in line. But standards are also on the rise; therefore, if you are considering buying a home, be aware that some lenders have tightened their standards.
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    • Many schools are unlikely to return to a normal schedule this fall, requiring continued online learning, impromptu childcare and stunted work days. California’s two largest public school districts – Los Angeles and San Diego – said on July 13 that this instruction will be remote only in the fall, citing concerns that the emergence of coronavirus infections in their areas poses a very serious risk for students. and teachers. Together, the two districts enroll about 825,000 students. So far, they are the largest in the country to abandon plans for partial physical return to classrooms when they reopen in August. For other districts, the solution will not be an all-or-nothing approach. Many systems, including the nation’s largest, New York City, are planning hybrid plans that involve spending a few days in classrooms and other days online. There is still no national policy, so check the municipal school system regularly to see what is happening in your community.
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    • Coronavirus can remain in the air for hours in small droplets in the stagnant air, infecting people while inhaling, suggest growing scientific evidence. This risk is highest in enclosed spaces with poor ventilation and can help explain over-dissemination events reported in meat-packing factories, churches and restaurants. It is not clear how often the virus is transmitted by these small droplets, or aerosols, compared to larger droplets that are expelled when a sick person coughs or sneezes or is transmitted by contact with contaminated surfaces, said Linsey Marr, an aerosol specialist from Virginia. Tech. Aerosols are released even when a person without symptoms exhales, speaks or sings, according to Dr. Marr and more than 200 other experts, who outlined the evidence in an open letter to the World Health Organization.
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  • Does the asymptomatic transmission of Covid-19 happen?

    • So far, the evidence seems to show that it is. A widely cited paper published in April suggests that people are more infectious about two days before the onset of coronavirus symptoms and estimated that 44% of new infections were the result of the transmission of people who still had no symptoms. Recently, a leading expert at the World Health Organization declared that transmission of coronavirus by people who had no symptoms was “very rare”, but later returned to that statement.

In the new analysis, a team led by Parham Azimi, an indoor air researcher at the Harvard School of Public Health TH Chan, studied the outbreak at the Diamond Princess, where physical spaces and infections were well documented. He performed more than 20,000 simulations of how the virus may have spread throughout the ship. Each simulation made a variety of assumptions about factors such as patterns of social interaction – how long people spent in their cabins, on deck or in the cafeteria, on average – and the amount of time the virus could live on the surface. Each also considered variable contributions from smaller and floating drops, generally defined as 10 microns or less; and larger drops, which fall more quickly and infect surfaces or other people, landing in the eyes, mouth or nose, for example.

About 130 of these simulations reproduced, to some extent, what actually happened at Diamond Princess as the outbreak progressed. In analyzing these more “realistic” scenarios, the research team calculated the most likely contributions from each transmission route. The researchers concluded that smaller droplets predominated and accounted for about 60% of new infections, both within a short distance, a few meters from an infectious person, and at greater distances.

“A lot of people have argued that overhead transmission is going on, but no one had numbers for that,” said Azimi. “What is the contribution of these small droplets – is it 5% or 90%? In this article, we provide the first real estimates of what that number would be, at least for this cruise ship. “

The logic behind this transmission is straightforward, experts said. When a person is speaking, he emits a cloud of droplets, the vast majority of which are small enough to remain suspended in the air for a few minutes or more. By inhalation, the cloud of small droplets is more likely to reach a mucous membrane than larger ones that fly ballistically.

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