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London, May 20: The current physical distancing guidelines of 6 feet may be insufficient to prevent COVID-19 transmission, according to a study which says a mild cough in low wind speeds can propel saliva droplets by as much as 18 feet.

Researchers, including those from the University of Nicosia in Cyprus, said a good baseline for studying the airborne transmission of viruses, like the one behind the COVID-19 pandemic, is a deeper understanding of how particles travel through the air when people cough.

In the study, published in the journal Physics of Fluids, they said even with a slight breeze of about four kilometres per hour (kph), saliva travels 18 feet in 5 seconds.

"The droplet cloud will affect both adults and children of different heights," said study co-author Dimitris Drikakis from the University of Nicosia.

According to the scientists, shorter adults and children could be at higher risk if they are located within the trajectory of the saliva droplets.

They said saliva is a complex fluid, which travels suspended in a bulk of surrounding air released by a cough, adding that many factors affect how saliva droplets travel in the air.

These factors, the study noted, include the size and number of droplets, how they interact with one another and the surrounding air as they disperse and evaporate, how heat and mass are transferred, and the humidity and temperature of the surrounding air.

In the study, the scientists created a computer simulation to examine the state of every saliva droplet moving through the air in front of a coughing person.

The model considered the effects of humidity, dispersion force, interactions of molecules of saliva and air, and how the droplets change from liquid to vapour and evaporate, along with a grid representing the space in front of a coughing person.

Each grid, the scientists said, holds information about variables like pressure, fluid velocity, temperature, droplet mass, and droplet position.

The study analysed the fates of nearly 1,008 simulated saliva droplets, and solved as many as 3.7 million equations.

"The purpose of the mathematical modelling and simulation is to take into account all the real coupling or interaction mechanisms that may take place between the main bulk fluid flow and the saliva droplets, and between the saliva droplets themselves," explained Talib Dbouk, another co-author of the study.

However, the researchers added that further studies are needed to determine the effect of ground surface temperature on the behaviour of saliva in air.

They also believe that indoor environments, especially ones with air conditioning, may significantly affect the particle movement through air.

This work is important since it concerns safety distance guidelines, and advances the understanding of the transmission of airborne diseases, Drikakis said.

Jun 2: Pakistan's COVID-19 cases reached 76,398 on Tuesday after 3,938 new infections were reported across the country, while the death toll due to the coronavirus has gone up to 1,621, according to the health ministry.

The Ministry of National Health Services said that 78 COVID-19 deaths were recorded in the last 24 hours, taking the total number of fatalities in Pakistan to 1,621.

A total of 27, 110 people have recovered, it said.

Sindh has 29,647 patients, Punjab 27,850, Khyber-Pakhtunkhwa 10,485, Balochistan 4,514, Islamabad 2,893, Gilgit-Baltistan 738 and Pakistan-occupied Kashmir 271, it added.

The authorities have conducted 577,974 tests, including 16,548 in the last 24 hours.

The jump in the number of cases comes a day after Prime Minister Imran Khan said that people should learn to live with COVID-19 until a vaccine is developed.

Khan addressed the media after chairing the meeting of National Coordination Committee, the highest body to tackle the pandemic.

"Coronavirus will not go away until the vaccine is discovered. We need to learn to live with it and we can live with it if we follow precautions," he said.

He said the one million volunteers of the government's coronavirus force will raise awareness of the need to follow guidelines.

The government also said that all sectors will be opened slowly after deciding the negative list of businesses which will not be allowed.

Beijing, Mar 21: China reported no domestically transmitted coronavirus cases for the third consecutive day even as seven more fatalities have been confirmed, taking the death toll in the country to 3255.

No new domestically transmitted cases of COVID-19 were reported on the Chinese mainland for the third day in a row on Friday, China's National Health Commission (NHC) said on Saturday.

The overall confirmed cases on the mainland had reached 81,008 by the end of Friday, which included 3,255 who died, 6,013 patients still undergoing treatment, 71,740 patients who had been discharged after recovery, the NHC said.

The NHC said 41 new confirmed COVID-19 cases were reported on the Chinese mainland on Friday from the people arriving from abroad, taking the total number of imported cases to 269.