Norovirus

Norovirus is a genus of viruses of the family Caliciviridae. Recent scientific findings reveal that the genus causes around 50% of all gastroenteritis (stomach pain, diarrhea, and vomiting) around the world.[1] It is considered the most important group of viruses associated with this condition. The prototype virus of the genus is the Norwalk virus; in fact, the genus was once referred to as Norwalk virus group or Norwalk-like viruses. Today, Norovirus may popularly refer either to the entire group of viruses or just Norwalk.

http://en.wikipedia.org/wiki/Norovirus