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Friday, July 10, 2020

How coronavirus spread in a restaurant shows why air travel is safer than you think

Over a period of one and a half meters and avoiding confined spaces, there are of course concerns about the health safety of air travel where passengers are crowded together on a plane.

Some may see a parallel in a limited study of how a restaurant in Guangzhou, southern China, was frequented by a Wuhan restaurant unknowingly infected with the coronavirus. Nine others around the diner have become infected. The shared meal was on January 24 when the spread of the virus was limited and the other diners had no other known exposure.

Airlines are planning to block the intermediate seat on flights so that passengers are spaced apart, but the restaurant study seems to show that social distancing has limits.

Image above: case-patient index indicated by a red circle filled with yellow. The red circles indicate the disposition of future patients. The dates are when the diagnosis was confirmed.

Of the other nine diners who subsequently became infected, two were on the immediate right side of the diner at the same table – an easy topic for social distancing. Yet two other infections occurred at diners 10 feet apart at a separate table.

“The key factor for the infection was the direction of the air flow,” researchers from the Guangzhou Center for Disease Prevention and Control concluded in a research letter to be published in July. Emerging infectious Illnesses journal published by the US Centers for Disease Control and Prevention.

The role of air flow and ventilation is relevant for aircraft. The case study restaurant had no windows and depended on air conditioners that ingested air from the room and then put it back out.

“The transmission of viruses in this outbreak cannot be explained by the transmission of droplets alone. The larger respiratory droplets only remain in the air for a short time and travel only for short distances, “they said.” However, a strong flow of air from the air conditioner may have propagated the droplets. “

Aircraft are commonly considered to be the restaurant: stale from the use of recycled air. However, the direction of the air flow is different.

While the restaurant’s air conditioner caused the air to move horizontally on many tables and diners, the airflow in the aircraft cabin is vertical.

Air is dispersed in the upper part of the cabin and on the side walls. This is especially important when the air is cold but the outside is warm and the fog appears to be spreading from the top of the cabin. The air is then extracted from the cabin through the grills at the bottom.

“This design feature makes the direction of the air flow in the cabin substantially vertical, and the air flow in the horizontal direction of the fuselage is very small,” the Chinese civil service said in February. “Under normal circumstances, diseases will not pass through the aircraft’s air conditioning system.”

Air from an aircraft cabin is replaced every two to three minutes. The aircraft engines suck in fresh air and mix it with the cabin air that passes through a HEPA filter capable of capturing more than 99.97% of the micron particles, said the CAAC.

Researchers studying the restaurant case do not believe that the virus has spread from the air conditioner by sucking in contaminated air from the room and recycling it. Six deburring tests of the air conditioner were negative for SARS-Cov-2.

The researchers didn’t say if the restaurant’s air conditioner had a HEPA filter, but usually only the high-end or industrial ones have one.

“HEPA filters have shown good performance with particles the size of the SARS-Cov-2 virus,” the European Union Aviation Safety Agency advised aircraft operators in April.

While most aircraft use HEPA filters, EASA has recommended that aircraft without filters should “completely avoid the use of air recirculation in the cabin” by deactivating the recirculation fans.

CAAC told airports to increase terminal ventilation.

EASA suggests, but does not impose, that passengers have an empty seat between them. Carriers from Air New Zealand to Delta Air Lines

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EASA also recommends what would have been impractical at the restaurant: covering one’s face with a mask.

The Guangzhou case study tracked down three separate families sitting at nearby restaurant tables. In the middle was the person who had arrived from Wuhan the day before.

Incubation periods make the researchers suggests that three diners at one table have been infected by the main restaurant. The two families overlapped the restaurant for 53 minutes. It is also possible, the researchers note, that the primary diner only infected one diner at the other table and subsequently passed on the infection to two family members.

For the table with two infections, which overlapped the primary table for 73 minutes, one or both may have been from the primary infected diner.

Each table had at least one infected person from the main restaurant, which was “the only known source of exposure for those affected”.

Later, after going to the restaurant, the main diner went to the hospital. The four family members associated with the main restaurant may have been infected outside the restaurant, but the researchers did not offer an opinion.

The round tables were located 3.3 feet apart. The researchers tracked down 91 people – 83 customers and 8 staff members – who were in the restaurant. Of the 83 customers, 10 developed COVID-19 while the other 73 were quarantined for 14 days and did not develop systems. None of the staff were infected.

Researchers made three restaurant recommendations: temperature screening, increased distance between tables, and improved ventilation.

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