In my opinion, this is really the main reason why this virus is spreading globally. In fact, the average incubation period seems to be 5 days, which is already a lot. But apparently, some subjects had an incubation period up to 24 days, if correct, this is huge and the main reason why it suddenly raised in Italy. Imagine only one relatively social person in Italy, in 24 days he/she can probably meet at least 50 person directly and much much more if he/she goes to some public activities. Like SARS, it just need a few super-spreaders who aren't even aware of being sick, to start an epidemic.