Mark -- I'm sure the CDC is investigating that very idea. But it is also an interesting thought that terrorists might try something less lethal that still makes people very sick and would cause an economic loss (people cancelling cruise plans because they don't want to get sick.)
For those of you who don't know -- Norwalk virus is like an extremely intense, very nasty 48 hour flu. This is the course of symptoms:
Nausea and dizziness
Diarrhea and/or vomiting
Low grade fever
You can get dehydrated very easily, and that can cause secondary complications.
I couldn't keep anything down for twelve hours and I was so sick I was admitted to the University clinic overnight. Norwalk can spread from person to person by contaminated articles or it can be ingested from contaminated food. At University of Delaware it started with a batch of contaminated food delivered to at least two (possibly three) of four dining halls on campus, all of which were overwhelmed by a record on-campus resident group moving in at the same time. Food was cross-contaminated in the rush to feed everyone (I got sick from chicken, another person got sick from a hamburger, etc.) and then people returned to their dormitories and contaminated the bathrooms. We ended up with over 500 people sick on campus in one night. It was so bad that University Health Services sent instructions out to the RAs in the dorms to tell people what to do for minor symptoms; only those people who violently ill were admitted to the Clinic. I collapsed while trying to get a ride to UHS (the policeman who found me said "Oh no, not another one.") I was sick for much longer than two days because of the lasting effects of dehydration.
Obviously then I have an interest in reading about others who are suffering through the same thing. I can't imagine an entire cruise ship... urk.
Up, up and away!