"Sarah, call the lab," Elias said, his voice tight. "Tell them to stop looking for bacteria. Tell them we need a PCR for Sin Nombre Hantavirus."

For six days, Elias lived in the shadow of Bed 7. He watched the "cytokine storm"—the body’s own frantic, misguided attempt to fight—slowly recede. On the seventh morning, Leo’s kidneys began to make urine. On the ninth, he squeezed Sarah’s hand.

In Bed 7 lay Leo, a 28-year-old marathon runner who had come in forty-eight hours ago with nothing more than a "stubborn flu." Now, he was on maximum ventilator settings, his lungs appearing as a white-out on the X-ray—a phenomenon clinicians call "shock lung."