The call center on the 11th floor of this 19-story office building in downtown Seoul had a layout that would look familiar to many a white-collar worker: Long rows of shared desks line each side of the open floor, with a handful of smaller meeting rooms and private offices tucked into the corners. On February 25, one of the 216 people who worked on the floor started experiencing symptoms of coronavirus. Swiftly, a cluster of cases began to ping-pong across the office, until the government caught wind and the building was shut down.

The Korea Centers for Disease Control and Prevention tracked down anyone who lived in, worked in, or had visited the office and apartment development, revealing the path of the virus as it leapt from warm body to warm body. Of the more than a thousand people they tested, 97 had contracted Covid-19. Nearly all of them worked together on the 11th floor. An infection map released by researchers showed that one side of the room, filled with lines of tables where at least six employees sat on each side, was hit hardest. In all, 94 of the 216 densely-packed employees tested positive for the disease, the cases scattered across the office like a checkerboard.