In a glitzy Shanghai shopping district, about 40 people who happened to be at a Uniqlo store were informed that they would be spending the night there. A suspected COVID-19 case had been traced to the shop.

Elsewhere in the same city, Anna Rudashko was told to return to an office building she had visited for a meeting the day before. She spent 58 hours there with more than 200 strangers, waiting for test results.

Across China, in Shaanxi province, Zhao Xiaoqing was on a second date, visiting a man at his parents’ home, when local authorities locked down the neighborhood. She quarantined with them for nearly 30 days. (Fortunately, she said, "I got along well with his family.”)