As an anesthesiologist, Dr. Au is responsible for one of the most dangerous parts of tending to patients with the coronavirus: intubating those who can’t breathe. The procedure, which involves snaking a tube into the patient’s trachea, is so dangerous because it brings the doctor close to the patient’s mouth, which is constantly shedding the virus. Patients sometimes exhale or cough as the tube is inserted, which aerosolizes the virus, allowing it to hang in the air for several hours.

Last week Dr. Au intubated two patients with Covid-19. “You’re aware of every moment you’re in there,” she told me. “Ten seconds. Twenty seconds. Thirty seconds. You feel radioactive.”

“Have you seen the HBO show ‘Chernobyl?’ ” she asked. “There are invisible risks that trail you.”

Those invisible risks — a trace of the coronavirus under a fingernail or on a strand of hair — don’t give Dr. Au nightmares just because she is worried about her own health and that of her colleagues. It’s because waiting at home she has a husband and three children.