Quote Originally Posted by blue matt View Post
they think incubation period is a few days, so they might have come into contact in the departure airport, if we tested them on arrival they would still be negative
Completely false. We don't yet know at which stage positive tests may happen, it could happen during the incubation period.

The incubation period is the period between getting infected and getting symptoms. Since the virus can be transmitted before the onset of symptoms, it follows that people can be tested during incubation. The success of these tests is, as yet, to be determined.