The patients ranged in age from 22 to 92, with a median of 56 years, and were admitted to Zhongnan Hospital of Wuhan University from Jan. 1 to Jan 28. Many of them — 41 percent — were presumed to have caught the virus in the hospital, including 17 people who had been admitted for other illnesses, and 40 health care workers.

The patient who infected so many health workers had been placed in a surgical ward because of abdominal symptoms, and the coronavirus was not initially suspected. Four other patients in that ward also contracted the disease, presumably from the first patient.

The incident was a chilling reminder of the “super-spreaders” in outbreaks of other coronavirus diseases, SARS and MERS — patients who infected huge numbers of other people, sometimes dozens. The phenomenon is poorly understood and unpredictable, an epidemiologist’s nightmare. Super-spreaders led to considerable transmission of MERS and SARS inside hospitals.