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. The virus is transmitted by fecally contaminated food or water, by person-to-person contact, and via aerosolization of vomited virus and subsequent contamination of surfaces. 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.
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. 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. 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.
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. This immunity does not fully protect against infection with the other diverse genotypes of the virus.
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. Many norovirus outbreaks have been traced to food that was handled by one infected person.
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, and may be responsible for 50% of all foodborne outbreaks of gastroenteritis in the United States.