Norovirus, sometimes referred to as the winter vomiting bug in the UK and Ireland, is the most common cause of viral gastroenteritis in humans. It affects people of all ages.^[1] The virus is transmitted by fecally contaminated food or water, by person-to-person contact,^[2] and via aerosolization of vomited virus and subsequent contamination of surfaces.^[3] Annually, norovirus is associated with 906,000 outpatient visits in industrialized countries, with 64,200 inpatient hospitalizations. In developing countries, it is associated with 1.1 million hospitalizations, with an estimated 218,000 deaths.^[4]

Norovirus infection is characterized by nausea, vomiting, watery diarrhea, abdominal pain, and in some cases, loss of taste. A person usually develops symptoms of gastroenteritis 12 to 48 hours after being exposed to norovirus.^[5] General lethargy, weakness, muscle aches, headaches, and low-grade fevers may occur. The disease is usually self-limiting, and severe illness is rare. Although having norovirus can be unpleasant, it is not usually dangerous and most who contract it make a full recovery within two to three days.^[6] On surfaces, norovirus is rapidly inactivated by either sufficient heating or by chlorine-based disinfectants and polyquaternary amines, but the virus is less susceptible to alcohols and detergents.^[7]

After infection, immunity to the same strain of the virus – the genotype – protects against reinfection for between 4.1 (95% confidence interval [CI] 3.2–5.1) to 8.7 (95% CI 6.8–11.3) years.^[8] This immunity does not fully protect against infection with the other diverse genotypes of the virus.^[8]

Outbreaks of norovirus infection often occur in closed or semiclosed communities, such as long-term care facilities, overnight camps, hospitals, schools, prisons, clubs, dormitories, and cruise ships, where the infection spreads very rapidly either by person-to-person transmission or through contaminated food.^[9] Many norovirus outbreaks have been traced to food that was handled by one infected person.^[10]

The genus name Norovirus is derived from Norwalk virus, the only species of the genus. The species causes approximately 90% of epidemic nonbacterial outbreaks of gastroenteritis around the world,^[11] and may be responsible for 50% of all foodborne outbreaks of gastroenteritis in the United States.