Timeline of key events in the spread of the new coronavirus

JAN. 3: The number of cases of a new type of viral pneumonia in central China rises to 44 in an outbreak that awakens fearful memories of the 2002-2003 SARS epidemic. Most of the cases are traced to the South China Seafood City market in the suburbs of sprawling Wuhan, where offerings are reported to include wild animals.

JAN 9: Chinese state media report that a preliminary investigation of viral pneumonia in the city of Wuhan has identified a new type of coronavirus. Local authorities report 59 people with the illness.

JAN. 11: Health authorities in Wuhan report the country's first death from the new coronavirus.

JAN. 20: The head of a Chinese government team says human-to-human transmission has been confirmed in an outbreak of the coronavirus, a development that raises the possibility that it could spread more quickly and widely.

JAN. 21: Face masks sell out and air and rail passengers are checked for fever as China seeks to control the outbreak, which has reached four other countries and territories and threatens to spread further during the Lunar New Year travel rush. The U.S. reports its first case — a Washington state resident who recently returned from the outbreak's epicenter and was hospitalized near Seattle.

JAN. 22: Chinese state media report that the city of Wuhan has shut down outbound flights and trains as new virus keeps spreading.

JAN. 23: The World Health Organization says the viral illness in China that has sickened hundreds of people is not yet a global health emergency. The decision comes after Chinese authorities moved to lock down three cities and canceled major events in the capital, Beijing, during the Lunar New Year holiday period to try to contain the virus.

JAN. 24: China reports that the number of virus cases has increased to 1,287, and...