Norovirus is an RNA virus that causes approximately 90% of epidemic non-bacterial outbreaks of gastroenteritis around the world. It may also be responsible for 50% of all foodborne outbreaks of gastroenteritis in the U.S. It can affect people of all ages and is transmitted by food or water that is contaminated, by person-to-person contact, and through aerosolization of the virus and subsequent contamination of surfaces.

Immunity is usually incomplete and temporary after infection. People with blood type O are more often infected. Usually outbreaks occur in closed or semi-closed communities like long-term care facilities, overnight camps, hospitals, prisons, dormitories, and cruise ships. Many outbreaks have been traced to food that was handled by an infected person.

Heating or chlorine-based disinfectants rapidly inactivate the virus. It was originally named after the Norwalk agent which was found in Norwalk, Ohio. The genomes are similar to Caliciviridae family. Other names the illness goes by are winter vomiting disease, viral gastroenteritis, and acute non-bacterial gastroenteritis.

The virus multiplies in the small intestine of the infected person and symptoms will appear after 1 to 2 days. Acute gastroenteritis is the principal system and it usually develops between 24 and 48 hours after exposure and lasts between 24 and 60 hours. The disease is usually self-limiting, and characterized by nausea, vomiting, diarrhea, abdominal pain, and in some cases loss of taste.

The disease progressing to something sever is rare. The number of deaths in the US is estimated to be around 300 each year. Most of these deaths are the very young, elderly, and persons with weakened immune systems.

Polymerase chain reaction assays are routinely used for specific diagnosis. They are very sensitive and can detect concentrations as low as 10 virus particles. The ELISA test is available commercially but lacks specificity and sensitivity.

They are highly contagious with as few as ten virus particles being able to cause infection. Viruses continue to be shed after symptoms have subsided and shedding can still be detected many weeks after infection. Usually shellfish and salad ingredients are most often implicated in norovirus outbreaks. Hand washing is an easy and effective method to reduce the spread of norovirus pathogens. There is some research being done on a vaccine. A phase 1 trial began in 2007.