Bloomberg Business reports cases of norovirus on three different cruise ships. In each case the disease affected fewer than 150 passengers, on ships that easily carry 10 times that many. They report people throwing up and experiencing diarrhea.
So, what is norovirus? It is the same highly contagious intestinal disease that cycles through our public schools. The sufferer feels like hell for 24 hours and sort of weak for another 12, then it's gone and you are well. The other DrC has had it twice, I've lucked out so far.
When I was young norovirus was called the "24 hour stomach flu." It lasted 24 hours and did afflict the stomach (and intestines) but was never an influenza.
Ships are particularly succeptible because "noro" is passed by touch. On shipboard you are forever touching railings, elevator buttons, door handles, chair backs, cutlery, glasses, serving ladles, etc.
The DrsC carry jellied alcohol and douse our hands before eating. Most ships now locate Purell dispensers outside all dining areas and some other areas as well. It seems to help.
Handy Hint: You can know a ship is threatened by norovirus when the serving ladles in the buffet are turned around so you no longer help yourself but must rely on ship's personnel to serve you. This is done for your protection when sick bay reports a few cases of noro.