Home » Covid, the WHO changes the rules of contagion: this is how the virus is transmitted

Covid, the WHO changes the rules of contagion: this is how the virus is transmitted

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Covid, the WHO changes the rules of contagion: this is how the virus is transmitted

It took us four years to understand that “Covid is transmitted through coughs and sneezes”, basically through the air, and that it wouldn’t have been much more useful to disinfect surfaces and hands, or sneeze into your elbows? All necessary precautions – according to the WHO (World Health Organization) – at the beginning of the global contagion from the SARS-CoV-2 virus, and even much later. But now the definition has been revised, given that the WHO itself has published a new document signed by all the world‘s CDC (Centers for Disease Prevention and Control) which changes the rules to achieve the same final result: avoiding contagion, in fact. “Nothing wrong with our behavior – he underlines Fabrizio Pregliasco, medical director of the Galeazzi Hospital in Milan -. The WHO simply made a clarification, let’s call it an in-depth analysis. But the result does not change: all the elements of survival of the virus are elements of contagion.”

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WHO rewrites the chapter on transmission of infections

Let’s see what’s new. Four years later, the WHO has revised the terminology that identifies the way in which respiratory infections are transmitted. He updated the definitions of airborne transmission of viruses, underlining how the latter plays an important role in the propagation of respiratory diseases. As a first consequence, the ventilation of closed environments is recognized as a fundamental element for preventing the spread of respiratory pathogens. A condition which, even well after the outbreak of the pandemic, was considered almost “secondary”, certainly underestimated and outclassed by other anti-contagion prescriptions.

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The three ways of transmitting the virus: by air

When we talk about the spread of a pathogen like the SARS-CoV-2 virus we have to think about how it can “travel” from one person to another. And the WHO identifies three different ones. The first is by air or inhalation, which is basically the main mode of transmission. In this case there is no longer a difference between small droplets that float (aerosols) or larger droplets that fall to the ground due to gravity (droplets), but we speak generically of infectious respiratory particles (IRPs, Infectious Respiratory Particles). A person emits respiratory particles of different sizes that can be inhaled and penetrate the upper respiratory tract of susceptible people, reaching the alveoli and lungs. Contagion by inhalation occurs over both long and short distances. Particles can accumulate remotely for hours.

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Contagion by impact with deposition.

Contagion occurs in this way: the particles emitted by an infected person, by gravity, are deposited on the mucous membranes (mouth, nose, eyes) of a susceptible person (the particles that were called droplets). But this type of transmission occurs only over short distances, the so-called “talking distance”.
As for the “contact” mode of transmission, it has been clarified that an infected person can transfer contaminated particles of any size and at any distance, generally through hands that come into contact with their own mucous membranes or through surfaces. The susceptible person can then become infected by touching the contaminated surface and putting their hands to their mouth, nose or eyes or by directly touching the hands of the virus-positive person on which infected particles have deposited.

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A web app to measure the risk of contagion

Precisely to evaluate how quickly the virus responsible for the Covid disease is able to move between people in close contact or not, the World Health Organization has made a web app available to everyone called ARIA (Indoor Airborne Risk Assessment), whose function is to calculate the risk of contagion (in this case from Covid, in its different variants).
The web app is able to work based on different scenarios, i.e. based on the size of the environment, the number of people present, the number of positive people, the use or not of masks and suggesting the necessary countermeasures to limit the risk of infection.

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Pregliasco: “We didn’t make a mistake, just the transmission terminology changes”

According to Pregliasco “between the rules on contagion followed to date and the new ones established by the WHO, the right measure lies in the middle”. “Over time, further investigation and clarification of the terminology adopted became necessary – he underlines -. In reality, it was always said that there was a double option: the SARS-CoV-2 virus is found in large and small particles. And the three types of contagion via the respiratory route are still valid today: by air (inhalation) by impact with deposition and by contact. So I wouldn’t say that we’ve done everything wrong, because even from a distance you can get infected.”
“The WHO highlights the role of airborne transmission of the virus, therefore the ventilation of rooms is an element to consider – concludes Pregliasco -. Let’s say that the importance of Covid transmission through the air has expanded, especially indoors. But the result does not change: all the elements of survival of the virus are elements of contagion.”

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