America's top immunologist told the nation on Sunday it should get ready to "hunker down," keep distance from others and work together to help prevent a further explosion is cases of Covid-19, the disease caused by the newly discovered coronavirus.

"Everybody has got to get involved in distancing themselves socially. If you are in an area where there is clearer community spread, you have to be much, much more intense about how you do that. That is where you get things (like) school closings," said Anthony Fauci, directorof the National Institute of Allergy and Infectious Diseases,to Chuck Todd on NBC News' "Meet the Press," according to a transcript of the interview.

The interview came on a day when the U.S. discovered -- after belatedly ramping up testing in the days prior -- that virtually every state had cases of Covid-19, more than 60 people across the country had died from it, and known infections climbed toward 3,300 -- with nearly 730 in New York alone. Worldwide, nearly 160,000 were believed to have been infected by the virus, with about half of those in China.

It also came after a volatile week in which events big and small got canceled, offices started work-from-home programs, stores were closing, and schools in many districts announced closings. But much of the cancellations and no-live-audience policies for sporting and political events came only after earlier word that there would be no cancellations and that risk of contracting the disease was low -- even in places it was clearly not.

The refrain "this is an emerging, rapidly evolving situation" was repeated throughout the week by local government officials and others, and by Friday, after the president announced a national emergency, panicked shoppers had emptied shelves in grocery stores in major cities and beyond.

"You dont want to be complacent. You always want to be ahead of the curve," warned Fauci on Sunday -- even as America proved it has been far behind other nations and lagging in response to the coronavirus when compared to prepared places such as Hong Kong, Singapore and Taiwan -- all of which were hit by SARS, another deadly coronavirus disease, nearly two decades earlier.

"People have had two months to pay attention and learn from places that shut this down -- Taiwan, Hong Kong, Singapore -- and places that have been tragic -- Italy, Iran, likely Spain and France to follow," saidDr. David N. Fisman, a professor of epidemiology at the University of Toronto, in an exchange by email with TheStreet earlier in the weekend, before Fauci's appearance on "Meet the Press."Dr. Fisman's university is currently working on a model for Covid-19 for Canadian populations and is now sharing the code with other nations such as Ireland. The project's aim is to help people make "good choices" about how to slow the epidemic.

As businesses quickly responded by cancelling events and changing policies and as schools closed in some districts and governors and mayors restricted gatherings, Dr. Fisman said "states and localities are leading by default."

"The business community gets this," he said, noting that major corporations appear to see the value in disease control -- "and god help us, I hope for investment in vaccines and prevention in the future."

By Friday, Walgreens(WBA) - Get Reportsaid it wouldoffer space outside of some stores such as in parking lots where health professionals will offer coronavirus testing and Apple(AAPL) - Get Reportsaid itwas closing all retail stores outside of China until March 27. By Saturday, Alphabet (GOOGLE) said it was partnering with the U.S. government to create an online site to answer questions about Covid-19 symptoms and testing, according to Reuters. On Sunday,Nike announced two-week closures of stores.

But many have criticized the federal government's tardiness to act.

"I think in the U.S. there's been a degree of 'decapitation' of the public health response, because the CDC seems to be hamstrung by the Trump administration. As I said to a friend today: The lack of testing could be either intentional incompetence, or the old fashioned regular kind of incompetence. But it's incompetence, and it's going to kill a lot of people."

Also on "Meet the Press" hospital leaders warned of the battle ahead to treat patients and prevent a national crisis as seen in China earlier and Italy and elsewhere now.

"Well, my concerns are I think we need to think about this in almost a war-like stance. My concern is that we have millions of healthcare workers around this country who are prepared to do battle against this virus, but I'm concerned that there are at least a couple of areas of supplies that they need in order to fight that virus as effectively as possible," said Dr. Peter Slavin, president of Massachusetts General Hospital to Todd. Slavin was concerned about the lack of testing and expressed hopes that private labs would step up testing.

The next week or two are going to be critical," added Slavin. "We've begun to see cases in this area, but we expect them to rise dramatically in the coming weeks.

Reports are even beginning to emerge of staff at some health care centers testing positive for the disease in the U.S., with at least two cases in Boston area hospitals reported over the weekend. In China, many thousands of health care workers ended up getting infected by the coronavirus, and in some cases sickening other patients.

Now, as the U.S. works to uncover just how far and wide the coronavirus has already spread here, many are looking for leadership on how they can stay safe.

"I think Americans should be prepared that they are going to have to hunker down significantly more than we as a country are doing," said Fauci, adding that "the golden rule that I say is that, when you think you are doing too much, you are probably doing enough or not enough. Aright, that is the thing you got to do. Dont want to be complacent. You always want to be ahead of the curve. But it depends on how far ahead of the curve you want to be. Dont even, for a second, think that I am saying we shouldnt -- I like to be criticized. When I say oh, you are being too overactive, that is good for me."

This story has been updated.

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Nation's Top Doc: Don't Be Complacent, Get Ready to 'Hunker Down' - TheStreet