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How the spread of covid-19 is one of the most controversial issues in this pandemic.
What does airborne mean?
What does airborne mean?Scientists distinguish respiratory infectious diseases into "airborne transmission"—transmitted by aerosols suspended in the air—and infectious diseases transmitted through other means, including larger “droplets”.
Aerosols are tiny liquid particles that come from the respiratory tract and are produced when a person exhales, speaks, or coughs.
In general, airborne diseases may be more contagious.
infection
But these two modes of transmission-air transmission or aerosol transmission and droplet transmission-are not necessarily mutually exclusive.
The World Health Organization recommends that aerosols are liquid particles with a diameter less than or equal to 5 microns.
Can covid-19 spread through the air?
Can covid-19 spread through the air?Some scientists doubt the transmission route of aerosols, because covid-19 does not seem to be as contagious as measles.
Sneezing and coughing usually produce larger liquid particles.
Despite these unknown factors, some case studies have shown that the air can spread SARS-CoV-2 to more than two meters away from the infected person.
The infectious particles carried in the air of the new crown pneumonia may be the cause of the spread of the virus.
The best explanation for the spread in this epidemic is through airborne transmission.
Lancet aerosol may be the main transmission route of SARS-CoV-2.
What is the WHO's view on the airborne transmission of covid-19?
On March 1, 2021, the World Health Organization released a roadmap for improving and ensuring good indoor ventilation in the context of covid-19.
However, the WHO initially insisted that it was impossible to spread SARS-CoV-2 through the air.
Call on the medical community and relevant countries and international institutions to recognize the possibility of covid-19 transmission through the air Call on the medical community and relevant countries and international institutions to recognize the possibility of covid-19 transmission through the air
Since March 2020, WHO has gradually changed its position.
SARS-CoV-2 Airborne transmission of SARS-CoV-2 can occur during medical procedures that produce aerosols.
For covid-19, the virus is mainly spread through close or direct contact, or surfaces that may be contaminated.
This is why it is not called an airborne virus.
For covid-19, the virus is mainly spread through close range or direct contact, or possibly contaminated surfaces.
This is why it is not called an airborne virus
In other words, the agency’s current view is that although covid-19 may spread the virus through aerosols, it is not the main way for SARS-CoV-2 to spread .
Although covid-19 may spread the virus through aerosols, it is not the main route of SARS-CoV-2 transmission.
How do governments view the airborne transmission of covid-19?
How do governments view the airborne transmission of covid-19?The British proposal states that covid-19 is “spread through air droplets and smaller aerosols,” and points out that infectious particles can “suspend in indoor air for a period of time, especially when there is no ventilation.
” The government's main focus The public safety message is "hands, face, space" to remind people to wash their hands, wear masks, and keep their distance.
Recently, "fresh air" has been updated to encourage people to gather outdoors.
Transmission occurs in poorly ventilated and enclosed spaces, and often involves activities that cause increased breathing, such as singing or exercising.
This environment and activity may lead to the accumulation of virus-carrying particles.
Australia and other countries do not mention airborne or aerosol transmission in their official guidelines on the mode of transmission of covid-19.
How can we prevent airborne transmission?
How can we prevent airborne transmission?The government’s recommendations include ventilation, such as opening windows, and avoiding enclosed spaces.
Japan emphasizes avoiding "3Cs": close contact and close dialogue in crowded places.
Some evidence can be obtained from model research.
In one of the studies, researchers estimated that the risk of infection in a poorly ventilated room is three times higher than in a room that changes air 10 times an hour.
Installing air filtration units, such as those with high-efficiency particulate air filters or specialized ventilation systems, may also help.
Catherine Noakes, a professor of built environmental engineering at the University of Leeds, believes this may be one of the reasons why some governments are reluctant to officially declare SARS-CoV-2 "airborne.
" "If you think that something spreads through the surface, it is easy to take precautions and tell everyone to wash their hands.
But if we say it is pending, it means some considerable capital investment in architecture and technology.
" Installation costs Larger systems also have an adverse effect on the environment.
Can masks prevent airborne transmission?
Can masks prevent airborne transmission?Some people claim that airborne transmission means that masks are ineffective, because virus-carrying aerosols may pass through the small holes in the mask cloth.
But Noakes said that if the wearer releases these particles, the high humidity inside the mask may help capture these particles.
Unlike N95 and other filter masks, if the aerosol is already suspended in the air, cloth masks may only provide limited protection against inhalation.
Tighter masks or wearing two masks may reduce aerosol emissions from one source and inhalation by recipients.
However, a loose mask will block or deflect most of the exhaled air, thereby reducing the speed of the air.
How does the air spread between outdoors and indoors compare?
How does the air spread between outdoors and indoors compare?There is a risk of covid-19 transmission outdoors, but the risk is lower compared to indoor environments.
In the summer of 2020, some people condemned the widely reported gatherings on British beaches, which they believed would lead to a surge in the spread of covid-19.
However, in February of this year, Mark Woolhouse, professor of infectious disease epidemiology at the University of Edinburgh, told lawmakers: “There has been no outbreak related to public beaches, and there has never been a covid-19 outbreak related to beaches anywhere in the world.
” The Republic of Ireland recently announced.
The data show that only 0.
1% of covid-19 cases are related to outdoor activities.
Babak Javid, an associate professor of medicine at the University of California, San Francisco, believes that various interventions provide protection, but it is also important to recognize that the risks of a particular environment may vary.
"If you wear a mask, you may be able to tolerate a shorter distance between people," If you are outdoors, you can be closer to people.
If you are indoors, the distance itself may not provide protection.
"
Original source
Covid-19: What do we know about airborne transmission of SARS-CoV-2? BMJ 2021; 373 doi: https://doi.
org/10.
1136/bmj.
n1030 (Published 22 April 2021)
org/10.
1136/bmj.
n1030 (Published 22 April 2021)
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