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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.

Melbourne, Mar 18: Australian Prime Minister Scott Morrison on Wednesday warned its citizens not to travel abroad and banned "non-essential" gatherings of 100 people or more as the government declared the deadly coronavirus, that has infected over 450 people in the country, a "human biosecurity emergency".

Prime Minister Morrison on Wednesday said Australians should abandon all overseas travel because of the coronavirus epidemic. There have been 40 new cases since Tuesday.

Of the 454 confirmed cases in Australia, 43 have recovered and 5 have died from the COVID-19, according to the official figures.

Morrison declared a national "human biosecurity emergency" and ordered a halt to "non-essential" indoor gatherings of more than 100 people, on top of an existing ban on outdoor events of more than 500.

He said, "We haven't seen this sort of thing in Australia since the end of the First World War. This is a once-in-a-100-year-type event," Morrison said.

"Life is changing in Australia, as it is changing all around the world. Life is going to continue to change. The travel advice to every Australian is do not travel abroad. Do not go overseas."

However, schools across the country were still to remain open.

Morrison said Australia should prepare for "at least six months" of disruption as health authorities attempt to get on top of the coronavirus.

"For those of you thinking about going overseas for the school holidays, don’t. Don't go overseas," he said.

Morrison said there would be no short-term, quick fix to deal with the COVID-19 crisis in Australia, and warned that "tens of thousands of jobs" could be lost.

Responding to the panic buying, the prime minister urged the public to "Stop hoarding."

"I can't be more blunt about it. Stop it. It is not sensible, it is not helpful and it has been one of the most disappointing things I have seen in Australian behaviour in response to this crisis," he said.

On Wednesday, the New South Wales recorded a massive jump in new 59 cases as travellers returned from overseas. The cases jumped from 210 to 269 in the past 24 hours, according to the media reports here.

Queensland's total number of confirmed cases stood at 94.

State Premier Annastacia Palaszczuk said it is now "a different world" from just last week.

For Victoria, the Premier Daniel Andrew said the government could also ban gatherings of fewer than 100 people, noting he could not rule out further changes.

Chief Health Officer Brett Sutton said the spike in cases has been due to people who have travelled overseas.

Sutton said that the transmission in Victoria was not because of community transition like Italy.

Sutton has continued to urge people to wash their hands, socially distance and stay home if they are unwell.

"These are critical measures to be applied regardless of the 100 and 500 threshold,” he said.

In Western Australia, Health Minister Roger Cook said four new coronavirus cases have been confirmed overnight, taking the State's total to 35.

McGowan also condemned panic buyers in supermarkets as "jerks, drongos and bloody idiots."

He said there was "plenty of food to go round" and no need for people to buy in excessive quantities.

The outbreak, which first emerged in China's Wuhan city last year, has marched across the globe, infecting 198,006 people and killing 7,948, according to a tracker maintained by the Johns Hopkins University.

A shrimp seller at the wet market in the Chinese city of Wuhan believed to be the centre of the coronavirus pandemic, may be the first person to have tested positive for the disease, a media report said on Saturday.

The report by the London-based Metro newspaper said that 57-year-old woman, named by the Wall Street Journal as Wei Guixian, was selling shrimp at the Huanan Seafood Market when she developed what she thought was a cold last December.

Chinese digital news outlet, The Paper has said that she may be epatient zero'.

Wei was told by doctors her illness was "ruthless" and other workers at the market had come to the Wuhan Union Hospital with the same symptoms, the Metro newspaper report quoted the outlet as saying.

"Every winter, I suffer from the flu, so I thought it was the flu," the woman was quoted as saying by The Paper news outlet.

The shrimp seller added that she believed she contracted the coronavirus from the shared toilet in the market.

She said the fatal disease would have killed fewer people if the government had acted sooner.

Wuhan Municipal Health Commission has confirmed that Wei was among the first 27 people to test positive for the coronavirus.

It said she was one of 24 cases with direct links to the market, the Metro newspaper reported.

Though Wei may be "patient zero", it does not mean she is the first person to have contracted the virus, added the Metro report.

Chinese researchers have claimed that the first person diagnosed with the airborne virus had no contact with the seafood market and was identified on December 1, 2019.

Wei was later quarantined when a connection was made between the bug and the market before recovering in January.

As of Saturday, the global number of coronavirus cases stood at 104,837 with 27,862 deaths, according to the latest update by the Washington-based Johns Hopkins University.

The US has the highest number of cases at 104,837, followed by Italy 86,498 and China 81,948.

Italy has recorded the highest number of fatalities with 9,134 deaths, followed by Spain and China, at 5,138 and 3,299, respectively.