If the outbreak gets even worse, the U.S. will need to take care of patients that are seriously ill outside the hospital, too. The military, FEMA, and even state emergency responders are experienced in setting up tent hospitals that can provide high levels of care, including surgery, in disasters or mass-casualty events. But they are not set up for a virus that can spread through the air. “In mobile hospitals, very rarely do you have a lot of negative-pressure rooms,” Lew Stringer, a former senior medical adviser to FEMA, says. The facilities are not usually designed with stringent infection-control measures in mind.

Besides the risk of transmission, many coronavirus patients are in hospitals because they need supplemental oxygen, which Toner says could be especially tricky to deliver in a field hospital. Typically, hospitals store their oxygen in tanks, which are connected through the building to patient rooms. The tanks are big. They are potential fire hazards. And they might require yards and yards of tubing to connect them to patients who need oxygen. Building modern field hospitals for a highly contagious disease is “not something that’s ever been done before,” Toner says. “We’ll have to figure it out.” These field hospitals will also need more of all the standard equipment: beds, IV lines, and personal protective gear for hospital staff.

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But regardless of where the beds end up, there may not be enough health-care workers to take care of the patients in them. “The question is how would we staff all these areas,” Noble says. The hospital is figuring out how to train doctors who don’t usually work in emergency care—for example, surgeons whose elective procedures were canceled. State and local authorities are also asking recently retired health-care workers to come back to work, but that’s a tough ask, because older people are also the most at-risk for COVID-19.

If things get really bad—if seriously sick patients are put in field hospitals and staff are stretched thin—care in the middle of a pandemic will suffer as a result. Health-care workers will have to conserve protective equipment for themselves and save ventilators for patients most likely to recover.

A decade ago, Cantrill was on a national committee that created the guidelines for hospitals trying to make it through a crisis. They debated, in the abstract, about how to ration scarce resources that could mean the difference between life and death. Now, for the first time in his career, those guidelines are about to get real. “You’d hoped it never gets here,” he told me, “but I think that’s where we are.”