Studies Show N.Y. Outbreak Originated in Europe

Studies Show N.Y. Outbreak Originated in Europe

The C.D.C. outlined how essential employees can go back to work even if they have been exposed. Scientists warn that the virus might not fade in warm weather.

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Coronavirus in New York came mainly from Europe, studies show.

New research indicates that the coronavirus began to circulate in the New York area by mid-February, weeks before the first confirmed case, and that it was brought to the region mainly by travelers from Europe, not Asia.

“The majority is clearly European,” said Harm van Bakel, a geneticist at Icahn School of Medicine at Mount Sinai, who co-wrote a study awaiting peer review.

A separate team at N.Y.U. Grossman School of Medicine came to strikingly similar conclusions, despite studying a different group of cases. Both teams analyzed genomes from coronaviruses taken from New Yorkers starting in mid-March.

The research revealed a previously hidden spread of the virus that might have been detected if aggressive testing programs had been put in place. On Jan. 31, President Trump barred foreign nationals from entering the country if they had been in China — the site of the virus’s first known outbreak — during the previous two weeks.

Viruses invade a cell and take over its molecular machinery, causing it to make new viruses. An international guild of viral historians ferrets out the history of outbreaks by poring over clues embedded in the genetic material of viruses taken from thousands of patients.

In January, a team of Chinese and Australian researchers published the first genome of the new virus. Since then, researchers around the world have sequenced over 3,000 more. Some are genetically identical to each other, while others carry distinctive mutations.

C.D.C. issues new back-to-work guidelines for essential workers.

The Centers for Disease Control and Prevention published new guidelines on Wednesday detailing how essential employees can go back to work even if they have been exposed to people infected by the coronavirus, provided they do not feel sick and follow certain precautions.

Those employees can return if they take their temperature before heading to their workplaces, wear a face mask at all times and practice social distancing while on the job, Dr. Robert Redfield, the C.D.C. director, said at the White House briefing. They should not share headsets or other objects that touch their faces, and they should not congregate in break rooms or crowded areas, he said.

Dr. Redfield said that employers should send workers home immediately if they developed any symptoms. He also said they should increase air exchange in their buildings and clean common surfaces more often. The goal, he said, was to “get these workers back into the critical work force so that we don’t have worker shortages.”

The new guidance appears to blend earlier advice. Last week, the C.D.C. recommended that even healthy Americans wear masks in public after data showed as many as 25 percent of people infected with the virus were asymptomatic, at the urging of the White House, businesses, workers and others to kick-start the idled economy.

Dr. Deborah Birx, the White House’s coronavirus response coordinator, and other government experts suggested at the briefing that the strict measures being taken by Americans to stem the spread of the virus may be leveling new cases in areas like New York, Detroit, Chicago and Boston.

In New York, ‘the bad news is actually terrible.’

New York, the hardest hit state in America, reported its highest number of coronavirus-related deaths in a single day on Wednesday, announcing that another 779 people had died. That brought the virus death toll to 6,268 in New York State, which Gov. Andrew M. Cuomo noted was more than twice as many people as the state had lost in the Sept. 11, 2001, attacks.

“I went through 9/11,” he said at his daily briefing. “I thought in my lifetime I wouldn’t have to see anything like that again — nothing that bad, nothing that tragic.”

The number of hospitalizations had fallen in recent days, he said, suggesting that social distancing measures were working to flatten the steep curve of the virus’s spread, at least for now. The rates depend not only on the number of new arrivals but also on hospital admission standards.

“If we stop what we are doing, you will see that curve change,” Mr. Cuomo warned.

Then he pivoted to a more somber tone. “The bad news isn’t just bad,” he said. “The bad news is actually terrible.”