Norovirus infection

Noroviruses are a group of viruses whose genetic material is RNA and that have no envelope, meaning they lack the fatty layer that surrounds other viruses. They belong to the Caliciviridae family and are the leading cause of acute gastrointestinal illness worldwide.

What they cause is recognizable: nausea, vomiting, diarrhea and abdominal pain. The real danger lies not in each symptom on its own but in what they add up to, because that much fluid loss can lead to dehydration, and dehydration itself can require medical attention.

It is spread by the fecal-oral route, which is the blunt way of saying that particles of the virus leave one person's stool and end up entering another person's mouth. The most common way is from person to person, but it also spreads by drinking contaminated water or eating contaminated food, or by touching a contaminated surface. So the same chain of transmission can run through a person, through a glass of water, or through a surface someone touched.