Scenes from the national COVID-19 emergency in the United States

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From Hollywood to Wall Street, sports stadiums to Broadway, daily life in the U.S. ground to a halt this week in an unprecedented effort to stem the spread of the new coronavirus that has caused a global pandemic.

As President Donald Trump declared a national emergency Friday, governors in several states scrambled to close schools. Universities moved classes online. Companies ordered employees to work from home. Film studios announced that they would delay the release of major franchises, including James Bond and the Fast and the Furious.

In Washington, Capitol Hill was closed to visitors. Professional sports leagues announced that they were suspending the playing season, while the National Collegiate Athletic Association said it would scrap its annual March Madness basketball tournament.

In Silicon Valley, normally a 24-7 buzz of activity, the highways were deserted and grocery stores struggled to fill barren shelves as residents prepared to work from home. Apple, Google and Facebook announced that they would cancel annual conferences that attract thousands of developers from around the world.

From coast to coast, communities across the U.S. braced for a surge in cases of the novel coronavirus that has infected more than 137,000 people worldwide. Yet even as large swaths of U.S. society began to shut down Friday, medical experts warned that they were only beginning to understand the full scale of how far the virus has already spread.

State health officials confirmed nearly 1,700 cases and 41 deaths across the county, though those figures have been clouded by delays in testing. Medical experts now say that the United States may be only at the start of an outbreak rivalling the scale of outbreaks that have forced widespread lockdowns in Italy and China.

Researchers at the University of California, San Francisco last week estimated that as many as 70 per cent of Americans could eventually contract the virus, and 1.5 million could die.

“For everyone, the days of denial are over,” said San Francisco internist Dr. Jordan Shlain. He warned that concerns about a shortage of tests to detect the virus may soon give way to fears of a shortage of ventilators needed to keep a flood of newly sick patients alive.

The U.S. response to the pandemic has also been hampered by Mr. Trump’s early efforts to play down the threat of the coronavirus and by a patchwork of responses from state and local officials who have the task of deciding how to stem the spread of the virus in their communities.

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The U.S. reported its first confirmed case of COVID-19 on Jan 20. But on Friday, the COVID-19 Tracking Project, a group of researchers and journalists who compile official statistics, estimated that fewer than 16,500 people had been tested.

The Centers for Disease Control and Prevention sent out diagnostic test kits in early February. Lab workers soon reported that some tests were returning faulty results because of contaminated reagents – chemicals used to extract genetic materials from nasal swabs. Doctors also complained that the CDC’s test criteria were overly restrictive.

The Trump administration relaxed the requirements late last month and said it was planning to send out thousands of new test kits. But officials in California said that many patients were still awaiting tests last week because of a shortage of chemical reagents. Mr. Trump announced new efforts to speed up testing Friday.

Despite promises to screen more than 2,400 passengers who disembarked from the Grand Princess cruise ship, many said they were still waiting. “No one has been tested,” said Teresa Duncan Johnson, a cruise-ship passenger now in quarantine on a military base in Georgia, where some people were told they would have to restart the clock on their 14-day quarantine because new passengers had arrived. “They don’t have many answers.”

Ohio Governor Mike DeWine ordered all schools closed even though the state had recorded just five positive cases after Ohio public-health officials estimated that there may actually be more than 100,000 infected residents who had yet to be tested.

Responses to the pandemic have varied widely across the country. New York Governor Andrew Cuomo called in the National Guard to help monitor a “containment zone” set up around a synagogue in a suburb north of New York City that is the site of one of the country’s largest COVID-19 outbreaks.

In Washington State, where 31 people have died after the virus swept through Seattle-area nursing homes, Governor Jay Inslee issued a ban on gatherings of more than 250 people and closed schools in three counties hardest hit by the virus. He warned residents of the consequences of ignoring the restrictions. “The penalty is you might be killing your granddad if you don’t do it,” he said.

In California, which has reported more than 250 COVID-19 cases and four deaths, Governor Gavin Newsom banned large gatherings and issued an order allowing the state to commandeer hotels and medical facilities to quarantine patients. But he stopped short of closing schools, arguing that the move would harm low-income families who rely on in-school meals and burden parents whose jobs made it impossible to stay home from work.

“If you are a caregiver, a police officer, firefighter, emergency-room doctor, nurse, nurse practitioner, and you have kids, you may have no capacity to have those kids at home without your own presence being there,” Mr. Newsom said. Several school districts, including San Francisco, announced school closings anyway after parents complained.

Increasingly public-health officials in California acknowledge that the virus has likely already spread too far to contain through measures such as mandatory quarantines and detailed tracking of new cases. Instead, they have turned to simply urging the most vulnerable residents to stay home.

“The cat is already out of the bag,” said Peter Beilenson, health director in Sacramento County, which told residents last week that they no longer needed to self-quarantine for 14 days. “The community spread has already occurred.”