Take home point: Do not answer any intrusive questions
Whe you board a cruise ship these days, they all give you a health questionnaire to fill in and sign before you are allowed to embark.
It asks along the lines of: "Are you suffering from nausea or stomach problems, have you had a cold or flu-like symptoms in the last few days?".
This is to try and limit the spread of Norwalk and other viral outbreaks within the close community on board.
If you are rash enough to answer "Yes", a ship's medic will be on the scene within minutes to assess your condition and decide whether you are fit to travel.
If you have a temperature or any of the above symptoms you will be very likely be denied boarding and your vacation plans will be in ruins.
At least in that situation a qualified medic actually meets the traveller face to face, unlike in the case of this unfortunate family!