A highly contagious non-bacterial gastroenteritis, caused by calcivirus, a relatively recently discovered virus. The symptoms appear about 1-2 days after having been infected, as violent vomiting and diarrhea. The victim "first thinks he is going to die, then wishes he were dead, and then suddenly gets well", as one sufferer has put it. Relapses are not uncommon. The virus is spread by the carriers via foodstuffs or by direct contact. Washing your hands frequently is an important precautionary measure.
But it should be stressed that the virus does not multiply in the food, like bacteria do when it is warm in the summer, making the food "go bad". The food in itself may not be "bad" at all, it just transmits - most efficiently, we might add - the viruses that it has picked up from virus carriers who have been in contact with your smorgasbord.
Christmas bonus
Winter vomiting disease and the calcivirus are prevalent all over the world, but Swedes seem to be particularly hard hit by "Vinterkräksjuka", as the winter vomiting disease is called in Swedish. This is partly due to the popularity of "Julbord" (= "Christmas table"), a lucullan smorgasbord (or smörgåsbord, as it is spelled locally) served by nearly all restaurants during the weeks preceding Christmas. Most Swedish companies invite their personnel to eat "Julbord" (a treat worth about 50 euro/dollars) at a nice restaurant as a traditional Christmas bonus.
Virulent smorgasbord
From a hygienic point of view the "Julbord" is more of a bonus to the viral disease agents than to the restaurant guests. The food remains on the smorgasbord table for long periods of time and has ample opportunity to pick up viruses. It's all a matter of statistics and probability - the longer the food has been exposed, the greater the chance that a virus-carrier has had contact with it. So if you are invited to enjoy a "Julbord" at your favorite restaurant, take care! If it would be an insult to your host to decline the invitation, at least take some precautions:
- Choose an early sitting (= serving period), when the food on the serving table is still fresh
- Avoid cold dishes - these are most likely to have been on the table for a dangerously long time
- Avoid dishes with mayonnaise
- Most importantly - avoid a dessert called "Rice ā la Malta" - it has been implicated in many cases of "Vinterkräksjuka" (it has most likely been standing on the serving table since the restaurant opened in the morning)
Virus on board
Reportedly, the calcivirus has recently been implicated in outbreaks of vomiting disease on board Carnival and Disney cruise line ships in the US. The mechanism of infection is probably the same as in Swedish restaurants and their "Julbord" - food has been left exposed to calcivirus carriers for too long.
Reference:
Smittsskyddsinstitutet (= Swedish institute for the control of infectious diseases): www.smittskyddsinstitutet.se
Swedish dailies: Svenska Dagbladet (www.svd.se), Aftonbladet (www.aftonbladed.se) | 
