And sometimes, patients start to feel better before their health quickly deteriorates.

“That’s what we’re seeing with these patients who get a lot worse,” Lyn-Kew said. “They’re doing OK, and then all of a sudden they’re really fatigued, a lot more shorter of breath and having chest pains.”

In North Carolina, Dr. Christopher Ohl has also seen rapid, unexpected development of severe symptoms.

“They say, ‘Hey, you know, I think I’m getting over this,’ and then within 20 to 24 hours, they’ve got fevers, severe fatigue, worsening cough and shortness of breath, ” Ohl, an infectious disease expert and professor of medicine at the Wake Forest School of Medicine, said. “They they get hospitalized.”