How exactly can we catch the Coronavirus?

Six months after the beginning of the coronavirus crisis, the consensus on the central question is growing: how do people get caught by the Coronavirus?

It is not uncommon to catch covid-19 from a contaminated surface, scientists say. And short meetings with people outdoors are unlikely to spread the coronavirus.

Instead, the biggest culprit is close contact between people over long periods of time. Mass events, poorly ventilated areas and places where people speak loudly – or sing, in a familiar case – increase the risk.

These new discoveries help companies and governments prepare strategies for reopening, protecting public health as companies reopen. These include tactics such as placing Plexiglas compartments, asking people to wear masks in stores and elsewhere, using good ventilation systems, and keeping windows open when possible.

Two major recent studies have shown that mass quarantines – orders to sit at home, bans on large gatherings and the closure of companies – have prevented millions of infections and deaths worldwide. Now that we have more data, cities and states can introduce concrete measures to prevent the virus from reappearing, say scientists and public health experts.

That means better protection for residents of nursing homes and families where more generations live together in crowded homes, they say. It also means focusing on physical distance and masks and reducing the number of indoor gatherings.

“We don’t have to think about quarantine, but ways to increase physical distance,” said Tom Friedren, chief executive of the Life-Saving Resolution, a non-profit public health initiative. “Activities outside may be allowed, walking or cycling may be allowed while you are at a physical distance from all people, delivery from shops and other innovative methods that can facilitate the continuation of economic activity without re-igniting the epidemic.”

Recommendations for the reopening group include mass testing, contact monitoring, and isolation of infected or exposed individuals.

Recipe for infection

Covid-19 virus infection involves three steps:

1. Coughing, talking, and breathing create droplets of various sizes that carry the virus.

2. In order to cause an infection, you need to get enough virus or accumulate around you over time.

3. The virus must break down in the respiratory tract and use the ACE-2 receptors to enter the cells and multiply.

An important factor in transmission is that seemingly harmless activities such as talking and breathing create breathable pieces of different sizes that can burst through the air currents and potentially infect nearby people.

So far, health agencies have identified respiratory contact as the main mode of transmission of covid-19. These large drops of fluid can transmit the virus from one person to another if they come down to the eyes, nose or mouth. But they can fall to the ground or other surfaces fairly quickly.

Some researchers say the new coronavirus can also be transmitted through aerosols, or tiny droplets that float in the air longer than large droplets. These aerosols can be inhaled directly.

This is what may have happened at a restaurant in Guangzhou, China, where an infected guest, who was not yet ill, transmitted the virus to five other people sitting at neighboring tables. Ventilation in the space was poor, and the exhaust system was turned off, according to a study that looked at the conditions in the restaurant.

Aerosolized virus from breathing in or talking to a patient may accumulate in the air over time, and a strong air leak from the air conditioner on the wall may have helped the particles begin to circulate in the air, say the study’s authors, which is not yet available. reviewed.

Proper ventilation of the places people visit and work in is very important, said Yuguo Li, one of the authors and professor of engineering at Hong Kong University. Proper ventilation – such as directing air to the ceiling and pumping it out, or bringing fresh air into the room – dilutes the amount of virus in the room, reducing the risk of infection.

Another factor is long exposure. It is generally defined as unprotected contact with someone for more than 15 minutes at less than 1.8 meters, said John Brooks, chief medical officer at the Center for Disease Control and Prevention. But that’s just a general rule, he warns. It can take much less time if a person sneezes or if there is another intimate contact that releases a lot of respiratory droplets, he said.

Super carriers

On March 10, at a church choir rehearsal in Washington State, 87% of those present were infected, said Lea Hamner, an epidemiologist at Skagit County’s Public Health Department and lead author of a study on an investigation that warned of the potential for “super-transferable” events. , in which one person or a small number of people infect many others.

During the two-hour rehearsal, choir members changed places four times, were densely packed indoors and were mostly older, and therefore more vulnerable to disease, she said. In total, 53 of the 61 participants in the trial were infected, including at least one person who had symptoms. Two died.

Several factors have contributed, Hamner said. When they sing, people can release a large number of large and small respiratory particles. In addition, singers breathe deeply, which increases the chance of inhaling infectious particles.

Change the rules

Based on this new picture of infection, some rules are changing. The standard procedure for someone who is tested positive is to put quarantine at home. Some cities provide free temporary housing and social services where infected people can stay on a voluntary basis so as not to transmit the virus to family members.

If the number of Covid-19 cases begins to rise dramatically as states reopen, “new, more comprehensive mitigation measures may be needed, such as those implemented in March.”

Some scientists say that although aerosol transmission actually occurs, it does not explain most infections. In addition, the virus does not appear to be abundant in the air.

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