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COVID-19: Smaller cough droplets may travel over 6 metres, says study

COVID-19: A single cough droplet can travel up to 6.6 metres, says study.

The researchers from Singapore incorporated important aspects of fluid physics to deepen the understanding of viral transmission.

A recent study by the scientists from A-STAR's Institute of High-Performance Computing in Singapore on the dispersion of coughs using airflow simulation has found that some smaller droplets, which are easily carried by the wind, can travel up to 6.6 metres and even further under dry air conditions. This comes amid a steady rise in COVID-19 cases in India.

A single droplet can travel up to 6.6 metres

The COVID-19 pandemic has led many researchers to study airborne droplet transmission in different conditions and environments.

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The research, published in the journal Physics of Fluids, found that a single 100-micrometre cough droplet under wind speed of 2 metres per second can travel up to 6.6 metres and even further under dry air conditions due to droplet evaporation.

Not just mask, even social distancing is extremely important

Talking about the study, author Fong Yew Leong stated that in addition to wearing a mask, we found social distancing to be generally effective, as droplet deposition is shown to be reduced on a person who is at least 1 meter from the cough.

The researchers used computational tools to solve complex mathematical formulations representing airflow and the airborne cough droplets around human bodies at various wind speeds and when impacted by other environmental factors.

They also assessed the deposition profile on a person at certain proximity. A typical cough emits thousands of droplets across a wide size range.

The scientists found large droplets settled on the ground quickly due to gravity but could be projected 1 metre by the cough jet even without wind.

Medium-sized droplets could evaporate into smaller droplets, which are lighter and more easily borne by the wind, and these travelled further, they said.

Biological considerations of virus

The researchers offer a more detailed picture of droplet dispersion as they incorporated the biological considerations of the virus, such as the non-volatile content in droplet evaporation, into the modelling of the airborne dispersion of droplets.

Stressing about the evaporated droplets, author Hongying Li said that an evaporating droplet retains the non-volatile viral content, so the viral loading is effectively increased. He further added that this means that evaporated droplets that become aerosols are more susceptible to be inhaled deep into the lung, which causes infection lower down the respiratory tract, than larger unevaporated droplets.

These findings are also greatly dependent on the environmental conditions, such as wind speed, humidity levels, and ambient air temperature, and based on assumptions made from the existing scientific literature on the viability of the COVID-19 virus, the researchers said.

The findings could be applied to designing environments that optimise comfort and safety, such as hospital rooms that account for indoor airflow and airborne pathogen transmission.

India fights COVID-19

Active COVID-19 cases in India have been witnessing a steady decline and remained below six lakh for the sixth consecutive day on Wednesday due to a sustained fall in the mortality rate and a large number of patients recuperating from the disease daily, the Union health ministry said.

There are 5,33,787 active cases of coronavirus infection in the country as on date which comprise only 6.42 per cent of the total caseload, while the total number of recoveries has surged to 76,56,478 pushing the national recovery rate to over 92 per cent.

Sixteen states and Union Territories, including Assam, Punjab, West Bengal,Gujarat, Jharkhand, Rajasthan, Uttar Pradesh, Madhya Pradesh and Bihar, have cases per million lower than the national average, the ministry said.

(With inputs from Agencies)

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