[ad_1]
But there have been times when this advice didn’t work. In a Chinese restaurant, contaminated air blowing out of an AC vent infected diners at three separate tables. In the US, 52 choir members fell ill with Covid-19 after practising together in a hall. Other countries reported similar cases and it started looking like the coronavirus could hang around in the air.
Last month, 239 scientists and engineers wrote an open letter to the WHO, asking it to accept the possibility of Covid’s “airborne” spread. Shortly after that, WHO agreed “short-range aerosol transmission” of Covid cannot be ruled out, which means, in some situations you might get Covid without being physically close to a patient or getting coughed and sneezed at. Note that the WHO didn’t say it’s the main mode of transmission but only a possibility.
WHO says even if an infected person coughs or sneezes, droplets that shoot out of their nose and mouth quickly fall to the ground, and you will be relatively safe if you keep distance
DROPLETS & AEROSOLS
WHO’s updated advice comes with many riders. It says this kind of ‘infected air’ situation can only arise indoors when the ventilation is poor, the place is crowded and people spend a long time inside. Peeking inside the Washington choir hall, for instance, would not have made you sick.
It also uses the term “aerosol transmission”. What is an aerosol? Modern scientists don’t distinguish between droplets and aerosols. An aerosol is a particle in the air, and a droplet is just a liquid aerosol, they say.
But the WHO follows an old distinction. It says a droplet is an aerosol only if it is smaller than 5 microns in size. A micron is a thousandth part of a millimetre, yet wide enough to fit 10 Covid viruses side by side. A human hair is about 50 microns wide. When very fine droplets shoot out of a patient’s mouth and nose, the liquid in them can evaporate completely before hitting the ground, leaving the germs to float around like dust in the air. And these floating germs can infect someone who is more than six feet away.
WHO adds that the ‘infected air’ situation can only arise indoors when the ventilation is poor
HOW CONTAGIOUS?
The question scientists grappled with for months was whether the coronavirus falls to the ground or floats like dust. Normally, germs that take the ‘dust’ or aerosol route — such as measles, chickenpox, and tuberculosis — are highly contagious. Each measles patient, for example, infects 12-18 persons.
Diseases that spread through heavier droplets — such as flu, common cold and whooping cough — are much less contagious because they require close contact. The coronavirus largely behaves like the latter germs, so classifying it as ‘airborne’ is problematic. However, now there is another explanation for why a ‘droplet infection’ can spread many feet away from a patient.
MIT researchers say a cough or sneeze can throw droplets up to 20 feet, while normal speech generates fine droplets that can remain suspended in the air for 10 minutes or more. The virus may also be present in the microscopic droplets that a patient emits during normal breathing. So, in a confined space like a hall, shop or office, the amount of virus in the air can build up and cause infections sometimes.
Covid is largely a disease spread through close contact with patients
WHAT SHOULD YOU DO?
Despite the possibility of airborne transmission in confined and crowded spaces, Covid is largely a disease spread through close contact with patients. In the Washington choir case, the group spent 2.5 hours together in a hall. They sang for most of that time, which would have released a large quantity of viral particles. In the China restaurant case also, the diners were probably talking.
However, fears about the virus being ‘in the air’ are unfounded. You won’t get Covid from having tea in your balcony. You do need to be extra careful in indoor environments, though. Crowding can result in infection, poor ventilation increases its chances further. If people are shouting, singing or even talking, the risk goes up. If it’s necessary to visit such a place, wear a good mask and try to wrap up your work and get out quickly.
Source: Vox
[ad_2]
Source link