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Panic gripped big tech firms like Facebook and Twitter which decided to close their offices from Seattle to London as more employees tested positive for the new coronavirus.

Facebook shut its three London offices till Monday after an employee was diagnosed with COVID-19.

The social networking giant told nearly 3,000 employees in London to work from home after an employee, who is based in Singapore but visited the London offices between February 24-26, was diagnosed with the new coronavirus, Sky News reported on Friday.

"An employee based in our Singapore office who has been diagnosed with COVID-19 visited our London offices on February 24-26.

"We are therefore closing our London offices until Monday for deep cleaning and employees are working from home until then," the company said in a statement.

There have been 163 cases of coronavirus so far in the UK.

Earlier, Facebook recommended all its Bay Area employees in the US to work from home. The latest precautions come after San Francisco announced its first two coronavirus cases on Thursday.

Facebook has also shut its Seattle office until Monday after one of its contractors was confirmed to be infected with the virus. The infected contractor last visited the Facebook office on February 21. King County health officials said all Facebook sites should work from home until March 31.

Twitter shut its Seattle office for a 'deep clean' after an employee developed COVID-19 like symptoms though final result was still awaited.

"A Seattle-based employee has been advised by doctor about likely COVID-19, though still awaiting the final testing," Twitter said in a tweet on Friday.

"While the employee has not been at a Twitter office for several weeks and hasn't been in contact w/others, we're closing our Seattle office to deep clean," the company added.

According to The Seattle Times, at least 14 people have died due to COVID-19 in Washington State till date.

Amazon, Microsoft, Google and Facebook have advised their employees in Washington State to work from home.

Apple has reportedly suggested its employees at California campuses to work from home as an "extra precaution" while new coronavirus cases spread on the west coast in the US, especially Seattle area.

Apple's flagship developers' conference WWDC 2020 in June is also at the risk of getting cancelled as the Santa Clara public health department has warned against large public gatherings. The event draws nearly 5,000 developers from across the world.

The US death toll from the new coronavirus has climbed to 14, according to Johns Hopkins' tracker, with 329 cases reported across the country.

Feb 22: A 20-year-old Chinese woman from Wuhan, the epicentre of the coronavirus outbreak, travelled 400 miles(675 km) north to Anyang where she infected five relatives, without ever showing signs of infection, Chinese scientists reported on Friday, offering new evidence that the virus can be spread asymptomatically.

The case study, published in the Journal of the American Medical Association, offered clues about how the coronavirus is spreading, and suggested why it may be difficult to stop.

"Scientists have been asking if you can have this infection and not be ill? The answer is apparently, yes," said Dr. William Schaffner, an infectious disease expert at Vanderbilt University Medical Center, who was not involved in the study.

China has reported a total of 75,567 cases of the virus known as COVID-19 to the World Health Organization (WHO) including 2,239 deaths, and the virus has already spread to 26 countries and territories outside of mainland China.

Researchers have reported sporadic accounts of individuals without any symptoms spreading the virus. What's different in this study is that it offers a natural lab experiment of sorts, Schaffner said.

"You had this patient from Wuhan where the virus is, travelling to where the virus wasn't. She remained asymptomatic and infected a bunch of family members and you had a group of physicians who immediately seized on the moment and tested everyone."

According to the report by Dr Meiyun Wang of the People's Hospital of Zhengzhou University and colleagues, the woman travelled from Wuhan to Anyang on Jan. 10 and visited several relatives. When they started getting sick, doctors isolated the woman and tested her for coronavirus. Initially, the young woman tested negative for the virus, but a follow-up test was positive.

All five of her relatives developed COVID-19 pneumonia, but as of Feb. 11, the young woman still had not developed any symptoms, her chest CT remained normal and she had no fever, stomach or respiratory symptoms, such as cough or sore throat.

Scientists in the study said if the findings are replicated, "the prevention of COVID-19 infection could prove challenging."

Key questions now, Schaffner said, are how often does this kind of transmission occur and when during the asymptomatic period does a person test positive for the virus.

Washington, Apr 28: After nearly three weeks in an intensive care unit in Los Angeles, doctors treating 41-year-old Broadway actor Nick Cordero for COVID-19 were forced to amputate his right leg.

The flow of blood had been impeded by a blood clot: yet another dangerous complication of the disease that has been bubbling up in frontline reports from China, Europe and the United States.

To be sure, so-called "thrombotic events" occur for a variety of reasons among intensive care patients, but the rates among COVID-19 patients are far higher than would be otherwise expected.

"I have had 40-year-olds in my ICU who have clots in their fingers that look like they'll lose the finger, but there's no other reason to lose the finger than the virus," Shari Brosnahan, a critical care doctor at NYU Langone said.

One of these patients is suffering from a lack of blood flow to both feet and both hands, and she predicts an amputation may be necessary, or the blood vessels may get so damaged that an extremity could drop off by itself.

Blood clots aren't just dangerous for our limbs, but can make their way to the lungs, heart or brain, where they may cause lethal pulmonary embolisms, heart attacks, and strokes.

A recent paper from the Netherlands in the journal Thrombosis Research found that 31 percent of 184 patients suffered thrombotic complications, a figure that the researchers called "remarkably high" -- even if extreme consequences like amputation are rare.

Behnood Bikdeli, a doctor at New York-Presbyterian Hospital, assembled an international consortium of experts to study the issue. Their findings were published in the Journal of The American College of Cardiology.

The experts found the risks were so great that COVID-19 patients "may need to receive blood thinners, preventively, prophylactically," even before imaging tests are ordered, said Bikdeli.

What exactly is causing it? The reasons aren't fully understood, but he offered several possible explanations.

People with severe forms of COVID-19 often have underlying medical conditions like heart or lung disease -- which are themselves linked to higher rates of clotting.

Next, being in intensive care makes a person likelier to develop a clot because they are staying still for so long. That's why for example people are encouraged to stretch and move around on long haul flights.

It's also now clear the COVID-19 illness is associated with an abnormal immune reaction called "cytokine storm" -- and some research has indicated this too is linked to higher rates of clotting.

There could also be something about the virus itself that is causing coagulation, which has some precedent in other viral illnesses.

A paper in the journal The Lancet last week showed that the virus can infect the inner cell layer of organs and of blood vessels, called the endothelium. This, in theory, could interfere with the clotting process.

According to Brosnahan, while thinners like Heparin are effective in some patients, they don't work for all patients because the clots are at times too small.

"There are too many microclots," she said. "We're not sure exactly where they are."

Autopsies have in fact shown some people's lungs filled with hundreds of microclots.

The arrival of a new mystery however helps solve a slightly older one.

Cecilia Mirant-Borde, an intensive care doctor at a military veterans hospital in Manhattan, told AFP that lungs filled with microclots helped explain why ventilators work poorly for patients with low blood oxygen.

Earlier in the pandemic doctors were treating these patients according to protocols developed for acute respiratory distress syndrome, sometimes known as "wet lung."

But in some cases, "it's not because the lungs are occupied with water" -- rather, it's that the microclotting is blocking circulation and blood is leaving the lungs with less oxygen than it should.

It has just been a little under five months since the virus emerged in Wuhan, China, and researchers are learning more about its impact every day.

"While we react surprised, we shouldn't be as surprised as we were. Viruses tend to do weird things," said Brosnahan.

While the dizzying array of complications may seem daunting, "it's possible there'll be one or a couple of unifying mechanisms that describe how this damage happens," she said.

"It's possible it's all the same thing, and that there'll be the same solution."