“

However, the detection of three cases outside China is worrying. We calculate, based on flight and population data, that there is only a 1 in 574 chance that a person infected in Wuhan would travel overseas before they sought medical care. This implies there might have been over 1,700 cases in Wuhan so far, there are many unknowns, meaning the uncertainty range around this estimate goes from 190 cases to over 4,000. But the magnitude of these numbers suggests that substantial human-to-human transmission can not be ruled out. Heightened surveillance, prompt information sharing and enhanced preparedness are recommended.