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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.

Washington, Mar 31: The United States has performed over one million coronavirus tests so far, said President Donald Trump on Monday.

"Today, we reached a historic milestone in our war against coronavirus. Over 1 million Americans have now been tested, more than any other country by far, not even close," Trump said during a press briefing.

US Health Secretary Alex Azar said that approximately 100,000 samples are tested for coronavirus daily.

The number of novel coronavirus (COVID-19) cases within the United States surpassed 150,000 and the death toll has reached 2828, according to Johns Hopkins University. 

Rome, Mar 19: Italy on Wednesday reported 475 new deaths from the novel coronavirus, the highest one-day official toll of any nation since the first case was detected in China late last year.

The total number of deaths in Italy has reached 2,978, more than half of all the cases recorded outside China, while the number of infections stood at 35,713.

The previous record high of 368 deaths was also recorded in Italy, on Sunday. The nation of 60 million has now recorded 34.2 percent of all the deaths officially attributed to COVID-19 across the world.

With the death rate still climbing despite the Mediterranean country entering a second week under an effective lockdown, officials urged Italians to have faith and to stay strong.

"They main thing is, do not give up," Italian National Institute of Health chief Silvio Brusaferro said in a nationally televised press conference.

"It will take a few days before we see the benefits" of containment measures, said Brusaferro. "We must maintain these measures to see their effect, and above all to protect the most vulnerable."

Imposed nationally on March 12, the shutdown of most Italian businesses and a ban on public gatherings are due to expire on March 25.

But school closures and other measures, such as a ban fan attendance at sporting events, are due to run on until April 3.

A top government minister hinted Wednesday that the school closure would be extended well into next month, if not longer.

The rates within Italy itself remained stable, with two-thirds of the deaths -- 1,959 in all -- reported in the northern Lombardy region around Milan, the Italian financial and fashion capital.