The test came back positive that afternoon, Jan. 20, the first confirmed case in the U.S. By 11 p.m., the patient was in a plastic-enclosed isolation gurney on his way to a biocontainment ward at Providence Regional Medical Center in Everett, Washington, a two-bed unit developed for the Ebola virus. As his condition worsened, then improved over the next several days, staff wore protective garb that included helmets and face masks. Few even entered the room; a robot equipped with a stethoscope took vitals and had a video screen for doctors to talk to him from afar.

County health officials located more than 60 people who’d come in contact with him, and none developed the virus in the following weeks. By Feb. 21, he was deemed fully recovered. Somehow, someone was missed.

All the careful medical detective work, it’s now clear, wasn’t enough to slow a virus moving faster than the world’s efforts to contain it. In February, firefighters in Kirkland, Washington, began making frequent visits to a nursing home where residents complained of respiratory problems —evidence of continuing transmission that burst into public view a week ago when officials announced the first in a series of deaths at the facility from Covid-19, the disease caused by the virus.