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Spread of coronavirus infection and science of cough and sneeze

India Today logo India Today 26-03-2020 Prabhash K Dutta

Novel coronavirus spreads through droplets and mucus. These droplets and mucus come out when a person coughs or sneezes. A majority of droplets are tiny and remain suspended in air for some time.

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A typical cough begins with a deep breath during which lungs throw out compressed air with great thrust. Air jets out from mouth with crackles. On an average, a person throws out about one-and-a-half-litre of air in one cough. When we cough or sneeze, we also burst out saliva contaminated with viruses.

Scientists studying the mechanism of coughing and sneezing have found that around 3,000 droplets of saliva come out in a single cough. Some of the droplets of saliva travel at the speed of up to 80 kmph.

At this speed, you would not want to be in the range of somebody firing the shots of saliva at a time when the novel coronavirus pandemic is wreaking havoc everywhere on the planet.

Each droplet of saliva may contain up to 20 lakh novel coronavirus particles. Even if a few reach a healthy person's respiratory tract, the particles will colonise the person's body and multiply to billions in a week's time, when the infected individual would start showing symptoms of Covid-19.

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If coughing throws thousands of droplets of saliva or agents of infection, sneezing is its more virulent cousin.

Mechanically, a sneeze begins at the back of the throat, produces multiple times more droplets of saliva and generates much greater speed.

Typically, there could be up to 40,000 droplets of saliva in one sneeze of average strength. Many of these droplets, which have viruses and bacteria, travel at a speed of over 320 kmph.

Droplets coming out during a sneeze are generally smaller than those gushing out in a cough. This means they can deposit millions of viruses including novel coronavirus if coming from an infected person on to a healthy person, and thus increasing the chances of Covid-19 spread many times more.

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Gravity works to bring down most of the droplets on the earth's surface that we don't usually touch with our hands, and thankfully we don't tend to touch our nose, eyes or mouth. Still, some of the tiniest droplets stay in the air for a longer duration.

In the case of Covid-19, a study found that novel coronaviruses remain in air for few hours. They have not been found to travel longer distances in air, till now. But those attending to a patient or living in same breathing spaces as an infected person has more chance of inhaling these droplets and get infected.

In cases of many other viruses, such as those of influenza, the smaller droplets can become airborne again particularly in a closed environment such as a living room. The droplets evaporate under direct exposure of the sun.

Also watch: Streets across the globe emptied during Covid-19 lockdowns (Video by Time)

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At the same time, on certain surfaces such as plastic or steel, viruses survive for days. In the case of novel coronavirus, it was found to be active for three days on plastic and steel surfaces. 

Since it is everyone's habit to touch one's face, these droplets attach themselves on fingers and hands, which deposit them on all kinds of surfaces we touch. When we touch our faces with the same infected hands, we transport the virus at the entry gates of our respiratory tract, or the boiler plant of novel coronavirus.

This is the science that warrants an infected person to wear protective masks, and the rest to maintain distance and change the habit of touching one's face. Styaing clear of novel coronavirus is the best defence against Covid-19.

Follow the government's latest travel advice if you are planning a trip outside India or travelling back to India from affected areas. You can also read World Health Organization's advice on basic protective measures against the virus. WHO has also busted some myths surrounding coronavirus. The Ministry of Health's special helpline is available at +91-11-23978046 and ncov2019@gmail.com.

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