How will we know when it’s time to reopen the nation? Experts offer four benchmarks to watch for…..

Everyone wants to know when we are going to be able to leave our homes and reopen the United States. That’s the wrong way to frame it.

The better question is: “How will we know when to reopen the country?”

Any date that is currently being thrown around is just a guess. It’s pulled out of the air.

To this point, Americans have been reacting, often too late, and rarely with data. Most of us are engaging in social distancing because leaders have seen what’s happening in Europe or in New York; they want to avoid getting there; and we don’t have the testing available to know where coronavirus hot spots really are.

Since the virus appears to be everywhere, we have to shut everything down. That’s unlikely to be the way we’ll exit, though.

Some cities or states will recover sooner than others. It’s helpful to have criteria by which cities or states could determine they’re ready. A recent report by Scott Gottlieb, Caitlin Rivers, Mark B. McClellan, Lauren Silvis and Crystal Watson staked out some goal posts.

• Hospitals in the state must be able to safely treat all patients requiring hospitalization, without resorting to crisis standards of care.

Other cities and states fear that they will approach New York City’s state of crisis. They’re trying to increase the number of available beds and ventilators — as well as doctors, nurses and other health care providers — to make sure they aren’t overwhelmed in their capacity to provide care to all those who need it.

This is the most immediate bar, and the focus of most public health officials’ attention. At the moment, there’s no reason to believe any area is over a surge of cases, and analysts’ models predict many places won’t peak for weeks to come.

• A state needs to be able to test at least everyone who has symptoms.

Dr. Gottlieb and colleagues estimate that the nation would need to have the capacity to run 750,000 tests a week — this is after things have calmed down greatly. There are times we might need even more.

“The 750,000 number should be viewed as a reasonable expectation for when we haven’t been having any major pockets or regional outbreaks to manage,” said Mark McClellan, an author of the report and a professor of business, medicine and policy at Duke. “If more testing to help contain outbreaks and potential outbreaks is needed, which seems very plausible, especially early on, the number would need to be significantly larger. We’ll also have to do some surveillance of people without symptoms, especially in higher-risk settings.”

A national estimate means less in deciding whether a state can reopen than its local capabilities. A state would need to be sure it could test every single person who might be infected, and have the results in a timely manner. That would be the only way to achieve the next requirement.

• The state is able to conduct monitoring of confirmed cases and contacts.

A robust system of contact tracing and isolation is the only thing that can prevent an outbreak and a resulting lockdown from recurring. Every time an individual tests positive, the public health infrastructure needs to be able to determine whom that person has been in close contact with, find those people, and have them go into isolation or quarantine until it’s established they aren’t infected, too.

This will be a big challenge for most areas. Other countries have relied on cellphone tracking technology to determine whom people have been near. We don’t have anything like that ready, nor is it even clear we’d allow it. The United States also doesn’t have enough people working in public health in many areas to carry out this task.

Building that capacity will take significant time and money, and the country hasn’t even started.

• There must be a sustained reduction in cases for at least 14 days.

Because it can take up to two weeks for symptoms to emerge, any infections that have already happened can take that long to appear. If the number of cases in an area is dropping steadily for that much time, however, public health officials can be reasonably comfortable that suppression has been achieved, defined by every infected person infecting fewer than one other.

In suppression, cases will dwindle at an exponential fashion, just as they rose. It’s not possible to set a benchmark number for every state because the number of infections that will be manageable in any area depends on the local population and the public health system’s ability to handle sporadic cases.

“We wanted to suggest criteria that would allow locations to safely and thoughtfully begin to reopen, but what that looks like exactly will vary from state to state,” said Caitlin Rivers, another author of the report and an epidemiologist at the Johns Hopkins Center for Health Security. “We therefore included some flexibility for jurisdictions to tailor these criteria to their local context.”

These four criteria are a baseline. Other experts think we will need to add serological testing, which is different from the viral detection going on now. This type of testing looks for antibodies in the blood that our bodies created to fight the infection, not the infection itself. These tests can be much cheaper and faster than the ones we’re currently using to detect the virus in sick people.

Testing for antibodies will tell us how many people in a community have already been infected, as opposed to currently infected, and may also provide information about future immunity.

Gregg Gonsalves, a professor of epidemiology and law at Yale, said: “I’d feel better if we had serological testing, and could preferentially allow those who are antibody positive and no longer infectious to return to work first. The point is, though, that we are nowhere even near accomplishing any of these criteria. Opening up before then will be met with a resurgence of the virus.”

He added, “That’s the thing that keeps me up every night.”

Until we get a vaccine or effective drug treatments, focusing on these major criteria, and directing efforts toward them, should help us determine how we are progressing locally, and how we might achieve each goal.

It would also prevent us from offering false hope about when America can start reopening. Instead of guesses, people could have clear answers about when they might be able to go back to a closer-to-normal way of life.