This estimate of the number of cases in Wuhan is as of January 25, reported Dr. Gabriel Leung, chair of public health medicine at the University of Hong Kong, and colleagues. According to the World Health Organization's (WHO) figures, as of January 31 (18:00 Central European Time), there were 9,841 cases confirmed globally, including 9,720 in China.

Wuhan and the surrounding cities are under quarantine. The WHO has declared an international public health emergency, but it did not recommend travel or trade restrictions. In the U.S., the novel coronavirus outbreak was declared a public health emergency on January 31 and entry restrictions were imposed.

In explaining the huge difference in the modeling estimate versus official reports, Leung and colleagues noted the time lag between infection and the development of symptoms, the delay in medical attention, and the time it takes to confirm illness through lab tests.

The virus has spread out of Wuhan, and it's likely that other big Chinese cities, such as Beijing, now have their own localized outbreaks, the authors wrote. For populations outside of China, Leung and colleagues advocate immediate public health interventions in large cities that have close transport links to the country to avoid outbreaks.

"Independent self-sustaining outbreaks in major cities globally could become inevitable because of substantial exportation of presymptomatic cases and in the absence of large-scale public health interventions," they wrote. "Preparedness plans and mitigation interventions should be readied for quick deployment globally."

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