You've shelled out thousands to lock yourself inside a huge steel vault with one of the the most virulent pathogens known to science. Far from land, there is no chance of escape. Welcome to your nightmare vacation -- a cruise ship infected with the Norwalk Virus.

This deadly little chunk of RNA may be invisibly small, but it packs a powerful punch. Abdominal pain, vomiting and diarrhea will leave you ten pounds lighter -- a pale quivering shell of the former self that stepped aboard just a few days ago. Barricade yourself inside your cabin and live on boiled tea, but unless you are in the habit of inspecting every doorknob and faucet handle with an electron microscope, you will still have difficulty avoiding a germ so contagious that a mere 18 viruses is enough to resurface your digestive tract with something resembling corrosive lava -- often within 24 hours of contact. Antibiotics are useless. Noroviruses can survive freezing and remain alive on dry surfaces, water or fabric -- and are spread by feces or fresh vomit, a phenomenon that has been studied closely in restaurants.

Don't expect much sympathy from your kindly cruise ship doctor. Any sign of illness will have you padlocked inside your room, where you'll spend the rest of your trip soaking up bags of IV fluid and staring out your porthole at exotic ports of call while your friends improve their tans on deck. Take solace in knowing your captain is even more miserable. A norovirus infection can affect thousands of customers -- costing tens of millions to an industry already scarred by high profile disasters. Since norovirus is one of the most common causes of gastrointestinal distress -- affecting one in fifteen people a year -- the disease frequently eludes even the most stringent efforts at control, which is one reason those handsome cruise-ship officers always refuse to shake hands with you. A recent infection on the exclusive Queen Mary II sickened 200 people. Since there is no lasting immunity, they'll all be ready to catch a new strain next year. Have fun!

Fortunately, deaths are rare from Norovirus, and once the terror is over, you can share your awful experiences with your picky aunt who's always scrubbing the counter tops with rubber gloves and a Lysol-soaked sponge. After that trip, she may not seem so crazy after all.