Irrespective of how they came into the country, in a case where someone is incubating a disease, I think it could be a number of days, for example, before someone figured out exactly what was wrong with them. This is why the quarantine officer and the medical officers in the hospital, as Howard mentioned, would have to make an assessment of what illness this person is likely to have.
If they determine that this looks like a suspicious disease that could be contagious, that could be problematic irrespective of how they came into the country. Depending on what disease we thought we were dealing with, our epidemiologists would then be tracking people who had been exposed to this person, following up with them, having them medically examined, and then taking the appropriate containment measures.
Those procedures are already in place. We work very closely with our counterparts in other countries to do those kinds of things. Even if we're tracking people in another country, if we think they were potentially at risk, we provide information on travellers and who was exposed or who was sitting near somebody.