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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.

Shanghai, Jun 13: Authorities in Beijing have temporarily shut a major wholesale agricultural market following a rise in locally transmitted novel coronavirus infections in China's capital city over the past two days.

The closure of the Xinfadi wholesale market at 3 a.m. local time on Saturday (1900 GMT on Friday), came after two men working at a meat research centre who had recently visited the market were reported on Friday as having been infected by the novel coronavirus. It was not immediately clear how the men had been infected.

Concern is growing of a second wave of the new virus, even in many countries that seemed to have curbed its spread. It was first reported at a seafood market in Wuhan, the capital of central China's Hubei province, in December.

Beijing authorities had earlier halted beef and mutton trading at the Xinfadi market, alongside closures at other wholesale markets around the city.

Reflecting concerns over the risk of further spread of the virus, major supermarkets in Beijing removed salmon from their shelves overnight after the virus causing COVID-19 was discovered on chopping boards used for imported salmon at the market, the state-owned Beijing Youth Daily reported.

Beijing authorities said more than 10,000 people at the market will take nucleic acid tests to detect coronavirus infections. The city government also said it had dropped plans to reopen schools on Monday for students in grades one through three because of the new cases.

Health authorities visited the home of a Reuters reporter in Beijing's Dongcheng district on Saturday to ask whether she had visited the Xinfadi market, which is 15 km (9 miles) away. They said the visit was part of patrols Dongcheng was conducting.

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China reported 11 new COVID-19 cases and seven asymptomatic cases for Friday, the national health authority said on Saturday. And all six locally transmitted cases were confirmed in Beijing.

Wuhan, Jun 9: China on Tuesday dismissed as "incredibly ridiculous" a Harvard study, which pointed to a surge in traffic outside Wuhan hospitals from August 2019 suggesting that the coronavirus hit the area far earlier than reported.

A whitepaper on coronavirus released by China on Sunday said the virus was first noticed on December 17 and Chinese virologists confirmed human-to-human transmission on January 19, prompting authorities to impose lockdown of Wuhan from January 23.

US President Donald Trump and leaders of several countries have accused China of not being transparent in reporting the deadly disease, leading to huge human casualties and economic crisis across the world.

The new study by Harvard researchers says satellite images show an increase in traffic outside five hospitals in Wuhan from late August to December.

The traffic spike coincided with a rise in online searches for information on symptoms like "cough" and "diarrhoea".

China said the study was "ridiculous" and based on "superficial" information, BBC reported.

It is believed that the virus first appeared in China some time in November. Authorities reported a cluster of pneumonia cases with an unknown cause to the World Health Organization (WHO) on December 31.

"Clearly, there was some level of social disruption taking place well before what was previously identified as the start of the novel coronavirus pandemic," Dr John Brownstein, who led the research, told ABC news.

The study has not been peer-reviewed.

The researchers examined commercial satellite data from outside five Wuhan hospitals, comparing data from late summer and autumn 2018 to the same time period in 2019.

In one case, researchers counted 171 cars parked at one of Wuhan''s largest hospitals, Tianyou Hospital, in October 2018.

Satellite data from the same time in 2019 showed 285 vehicles in the same place, an increase of 67 per cent.

A surge in online searches for words associated with the symptoms of coronavirus on the Chinese search engine Baidu seemed to emerge at the same time.

"This is all about a growing body of information pointing to something taking place in Wuhan at the time," Dr Brownstein said.

"Many studies are still needed to fully uncover what took place and for people to really learn about how these disease outbreaks unfold and emerge in populations. So this is just another point of evidence," he said.

Asked for her reaction at the media briefing, Chinese Foreign Ministry spokeswoman Hua Chunying dismissed the findings as "incredibly ridiculous".

"I think it is ridiculous, incredibly ridiculous, to come up with this conclusion based on superficial observations such as traffic volume," she said.

"(I have) Not seen the research you mentioned. If the conclusion is drawn based on traffic volumes (and) other superficial observations, it won’t be a sound conclusion," she said and referred to the allegations about the COVID-19 originating from the Wuhan Institute of Virology (WIV) by Trump.

"That allegation was proved to be wrong," she said.

When pointed out that China says it respects science based inquiry and Harvard is one of the top universities in the world, Hua said, "on the origin of virus there are lot of conspiracy theories against China”.

"That is very unfair. At the moment, the pressing task is to enhance coordination to contain the spread of the virus. Someday, I am sure the truth will be out. China deserves a fair and objective evaluation," she said and referred to the whitepaper released by the Chinese government detailing evolution of coronavirus in Wuhan and how Beijing handled the situation.

Recently, the World Health Assembly (WHA), the decision-making body of Geneva-based World Health Organization (WHO), passed a resolution to probe the origin of the virus. China also backed the resolution.

As of Monday, the overall confirmed cases on the mainland had reached 83,043, including 58 patients who were still being treated, with no one in severe condition, China’s National Health Commission, (NHC) said.

Altogether 78,351 people had been discharged after recovery and 4,634 people had died of the disease, it said.