She’d been working nonstop for days at the center of China’s coronavirus outbreak, where she is a doctor. Both of her parents had Covid-19, the disease caused by the virus, as did many of her colleagues. The number of sick and dying was climbing. And on this day, Dr. Zhang had forgotten about her 9-year-old daughter, who was home alone and scared—and who, at that moment, wasn’t picking up the phone.

Dr. Zhang’s eyes welled up, but she had no energy to cry. “My tears wouldn’t flow,” she said in an interview on Feb. 18.

Around the world, doctors are being stretched to the limit. Short on supplies and sleep, they’re being asked to stop a global pandemic that no one fully understands. Adding to that strain, they’re risking their own health while they diagnose cases and attend to sick patients—along with the health of their spouses, children and other close family members…

In China, more than 3,000 doctors have been infected, according to official data, and at least 22 have died. Some medical professionals believe the numbers are even higher, adding uncertainty for doctors elsewhere confronting the virus. Untold numbers of family members have fallen ill.