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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, Jan 27: The death toll from a coronavirus outbreak in China rose to 81 on Monday, as the government extended the Lunar New Year holiday and more big businesses shut down or told staff to work from home in an effort to curb the spread.

Chinese Premier Li Keqiang visited the central city of Wuhan, the epicenter of the outbreak, as the government sought to signal it was responding seriously to the crisis.

The total number of confirmed cases in China rose about 30% to 2,744, about half of them in Hubei province, whose capital is Wuhan.

As worries grew around the world, Chinese-ruled Hong Kong, which has had eight confirmed cases, banned entry to people who had visited Hubei in the past 14 days. The ban did not cover Hong Kong residents.

The number of deaths from the flu-like virus in Hubei climbed to 76 from 56, health officials said, with five deaths elsewhere in China, including the southern island province of Hainan, which reported its first fatality on Monday.

While a small number of cases have been confirmed in more than 10 countries, linked to people who traveled from Wuhan, no deaths have been reported elsewhere.

Li is the most senior leader to visit Wuhan since the outbreak began. Clad in a blue protective suit and mask, he inspected efforts to contain the epidemic and spoke to patients and medical staff, the government said.

The government is extending the week-long Lunar New Year holiday by three days to February 2, in a bid to slow the spread of the virus. The Lunar New Year is usually a time for millions of people to travel, but many have had to cancel their plans because of travel curbs over the virus.

Incubation

Wuhan is already in virtual lockdown and severe limits on movement are in place in several other Chinese cities.

The city of 11 million clamped down further on Monday, announcing the suspension of visa and passport services until January 30.

Despite the curbs, the mayor of Wuhan said on Sunday that five million people had left the city for holidays and other reasons.

Images from Wuhan showing hospital corridors packed with people seeking treatment have circulated on social media, along with complaints of soaring prices for essentials such as vegetables.

Chinese leaders have urged transparency in the crisis, after public trust was eroded by the cover-up of the spread of Severe Acute Respiratory Syndrome (SARS), a coronavirus that originated in China and killed nearly 800 people globally in 2002 and 2003.

Much is not known about the newly identified coronavirus, including how easily it spreads and just how dangerous it is. It can cause pneumonia, which has been deadly in some cases.

National Health Commission minister Ma Xiaowei said on Sunday the incubation period could range from one to 14 days, and the virus was infectious during incubation, unlike SARS.

That compares with a World Health Organization (WHO) estimate of two to 10 days for the incubation period.

“Understanding the time when infected patients may transmit the virus to others is critical for control efforts,” the WHO said.

The virus is believed to have originated late last year in a Wuhan market illegally selling wildlife. It has spread to other cities, including Beijing and Shanghai, as well as more than 10 countries including France, Japan and the United States.

‘Overwhelmed’

Australia confirmed its fifth case on Monday involving a woman on the last flight out of Wuhan to Sydney before China’s travel ban.

Health minister Greg Hunt told the Australian Broadcasting Corporation (ABC) authorities aimed to get about 100 Australian children and young people out of Wuhan.

One father of two, Nathan Wang, told the ABC his wife was stuck in Wuhan with the children. “We absolutely want the children to come back, because hospitals in Wuhan are overwhelmed,” he said.

Airports around the world have stepped up screening of passengers from China, although some health experts have questioned its effectiveness.

Last week the WHO stopped short of calling the outbreak a global health emergency, but some health experts question whether China can contain the epidemic.

WHO Director-General Tedros Adhanom Ghebreyesus is due to travel to Beijing to meet officials and health experts.

Australia, France, Italy, Japan and the United States have all said they are working to evacuate citizens from Wuhan.

Some of China’s biggest companies have been affected, with hotpot restaurant chain Haidilao International Holding shutting branches nationwide from Sunday until Friday.

Gaming giant Tencent Holdings Ltd advised staff to work from home until February 7, and e-commerce firm Alibaba removed vendors’ offers of overpriced face masks from its online Taobao marketplace as prices surged.