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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.

Apr 26: The Chinese city of Wuhan, where the global coronavirus pandemic began, now has no remaining cases in its hospitals, a health official told reporters on Sunday.

"The latest news is that by April 26, the number of new coronavirus patients in Wuhan was at zero, thanks to the joint efforts of Wuhan and medical staff from around the country," National Health Commission spokesman Mi Feng said at a briefing.

The city had reported 46,452 cases, 56% of the national total. It saw 3,869 fatalities, or 84% of China's total.

Nairobi, Mar 14: Kenya and Ethiopia on Friday announced their first confirmed cases of coronavirus, as East Africa, which has so far been unscathed by the global pandemic, scaled up emergency measures to contain its spread.

In Kenya, a 27-year-old Kenyan woman tested positive for the virus on Thursday in Nairobi, a week after returning from the United States via London.

She was in a stable condition and recovering, Health Minister Mutahi Kagwe told reporters.

"We wish to assure all Kenyans that the government will use all the resources available to fight coronavirus," he said, as the government rolled out a raft of new containment measures.

The government had traced all the contacts of the patient since she arrived back in Kenya on March 5, he said.

"At the moment, there is absolutely no need for panic and worry," he said.

Kenya, with a population of 50 million people, saw a spree of panic buying among the middle-class in Nairobi supermarkets, in the wake of the announcement.

Meanwhile Ethiopia, Africa's second most populous nation with over 100 million people, said a 48-year-old Japanese man who had arrived in the country on March 4 from Burkina Faso was confirmed to have contracted the virus.

"He is undergoing medical follow-up and is in a stable condition. Those who have been in contact with this person are being traced and quarantined," the health ministry said in a statement.

Burkina Faso only confirmed its first case on Tuesday -- a couple returning from France -- and the Japanese patient had been in that country since February 24.

Ethiopian Health Minister Lia Tadesse said three other patients were in isolation.

Ethiopia becomes the 15 country in Africa with a confirmed case of the virus that has swept the globe, infecting more than 130,000 people and killing nearly 5,000 since it first emerged in China.

But to date the continent has been spared the worst of the pandemic.

Only five people have succumbed to coronavirus so far -- all in north Africa -- with the sub-Saharan region recording no deaths and very low numbers of confirmed cases.

But countries in East Africa -- which until the positive case in Kenya, had only recorded negative test results -- have been taking precautions.

Some flights have been restricted, with Kenya Airways suspending its route to Rome, and charter flights from Italy to the Kenyan coast on hold.

It has also suspended international conferences, a top earner in Nairobi, a hub for such events in the region, and non-essential travel abroad for politicians.

The government announced more expansive restrictions on Friday, including a temporary ban on major public gatherings, prison visits and activities between schools.

Other countries in the region have been rolling out their own measures.

In Rwanda, which shares a border with the Democratic Republic of Congo, which has confirmed cases, washing basins with soap and sanitiser have been placed on streets for commuters to use before boarding buses.

Authorities in Kigali, the capital, have also banned concerts, rallies and trade fairs -- although like in Kenya and Uganda, church services have been proceeding and bars, restaurants and entertainment precincts remain open.

Neighbouring Burundi, meanwhile, has quarantined 34 people in a hotel in Bujumbura as a precaution.

Uganda has ordered that visitors from a number of affected countries self quarantine for 14 days, or consider simply not visiting at all.

South Sudan's health ministry said meanwhile that it was "temporarily suspending direct flights between South Sudan and all affected countries".

Kagwe, the Kenyan health minister, also addressed a rumour circulating on social media that people with black skin cannot contract the virus.

"I would like to disabuse that notion. The lady (confirmed with coronavirus in Kenya) is an African, like you and I," he said.