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A World Health Organization (WHO) expert said on Monday that the alarm was triggered in Wuhan since there was a specific surveillance system in place in the region for picking up atypical pneumonia, which does not necessarily mean Wuhan is where the novel coronavirus transmitted from animals to humans.

Dr. Michael Ryan, executive director of the Health Emergencies Program of the WHO, made the remarks at a press conference.

What is required is going to be a much more extensive retrospective epidemiological study to look at those first cases in Wuhan and to fully understand the links between those cases, said Ryan, so that we can then determine whether the cross-species transmission of coronavirus happened in Wuhan or elsewhere.