Norovirus (formerly Norwalk agent) is an RNA virus (taxonomic family Caliciviridae) that causes approximately 90% of epidemic nonbacterial outbreaks of gastroenteritis around the world (Lindesmith et al. 2003), and may be responsible for 50% of all foodborne outbreaks of gastroenteritis in the United States (Widdowson et al. 2005; National Center for Infectious Diseases, CDC. 2011). Norovirus affects people of all ages. The viruses are transmitted by fecally contaminated food or water, by person-to-person contact (Goodgame 2006), and via aerosolization of the virus and subsequent contamination of surfaces (Said et al. 2008).

When a person becomes infected with norovirus, the virus begins to multiply within the small intestine. After approximately one to two days, norovirus symptoms can appear. The principal symptom is acute gastroenteritis that develops between 24 and 48 hours after exposure, and lasts for 24–60 hours (National Center for Infectious Diseases, CDC. 2011). The disease is usually self-limiting, and characterized by nausea, forceful vomiting, watery diarrhea, and abdominal pain, and in some cases, loss of taste. General lethargy, weakness, muscle aches, headache, coughs, and low-grade fever may occur.

Severe illness is rare: although people are frequently treated at the emergency ward, they are rarely admitted to the hospital. The number of deaths from norovirus in the United States is estimated to be around 300 each year, with most of these occurring in the very young, elderly, and persons with weakened immune systems. Symptoms may become life-threatening in these groups if dehydration is ignored or not treated (Goodgame 2006).

After infection, immunity to norovirus is usually incomplete and temporary (Lindesmith et al. 2005). Outbreaks of norovirus infection often occur in closed or semiclosed communities, such as long-term care facilities, overnight camps, hospitals, prisons, dormitories, and cruise ships, where the infection spreads very rapidly either by person-to-person transmission or through contaminated food (Noda et al. 2007). Many norovirus outbreaks have been traced to food that was handled by one infected person (Koopmans & Duizer 2004).

Norovirus is rapidly inactivated by either sufficient heating or by chlorine-based disinfectants, but the virus is less susceptible to alcohols and detergents, as it does not have a lipid envelope (Jimenez & Chiang 2006).