COVID-19 transmission via aerosol

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The U.S-based Centers for Disease Control and Prevention (CDC) acknowledged last week that people can sometimes become infected with the novel coronavirus through airborne transmission, especially in enclosed spaces with inadequate ventilation.
Now, the CDC is saying infection can also spread through exposure to smaller virus-containing droplets and particles that can remain suspended in the air over long distances and time.
“There is evidence that under certain conditions, people with COVID-19 seem to have infected others who were more than six feet away,” the updated site states. “These transmissions occurred within enclosed spaces that had inadequate ventilation. Sometimes the infected person was breathing heavily, for example, while singing or exercising.”
“Under these circumstances,” the site says, “scientists believe that the amount of infectious smaller droplets and particles produced by the people with COVID-19 became concentrated enough to spread the virus to other people. The people who were infected were in the same space during the same time or shortly after the person with COVID-19 had left.”
In a statement, the agency said it “continues to believe, based on current science, that people are more likely to become infected the longer and closer they are to a person with COVID-19.”
Experts have pointed to the spread of the virus in choirs, buses, fitness classes, and other poorly ventilated spaces. In July, more than 200 aerosol biologists and other experts sent a letter expressing concerns about airborne transmission to the World Health Organization, which responded by acknowledging the “emerging evidence” the pathogen can spread through the air.
The CDC says these are rare, and existing advice on protective behaviors – washing hands, wearing face coverings, and social distancing – remains the same.
“People can protect themselves from the virus that causes COVID-19 by staying at least six feet away from others, wearing a mask that covers their nose and mouth, washing their hands frequently, cleaning touched surfaces often and staying home when sick,” says the CDC.
How easily a virus spreads from person to person can vary. The virus that causes COVID-19 appears to spread more efficiently than influenza but not as efficiently as measles, which is among the most contagious viruses known to affect people.
Respiratory droplets cause infection when they are inhaled or deposited on mucous membranes, such as those that line the inside of the nose and mouth. As the respiratory droplets travel further from the person with COVID-19, the concentration of these droplets decreases. Larger droplets measuring more than five microns fall out of the air due to gravity. Smaller droplets less than five microns and particles spread apart in the air. With passing time, the amount of infectious virus in respiratory droplets also decreases.