This is going to be bad. Apparently, an infected person is contagious even before the symptoms showed up. Apparently, the incubation period is as short as 3 days. There’s a case where a (infected)father went abroad to visit his son and within 3 days the son got a high fever and is confirmed to have the virus. How many people did this man infect on the trip to visit his son (via bus/plane/train)?