The norovirus (previously called Norwalk-like virusî or NLV) is a member of the family Caliciviridae. The name derives from the Latin for chiliceócalyxómeaning cup-like, and refers to the indentations of the virus surface.
Nature has created an ingenious bug in Norwalk. The round blue ball actually is a protein surrounding the virus’s genetic material. The virus attaches to the outside of cells lining the intestine. Then it transfers its genetic material into that cell. There it reproduces, finally killing the human cell to release new copies of it that attach to more cells of the intestine’s lining.
The family of Caliciviridae consists of several distinct groups of viruses that were first named after the places where outbreaks occurred. The first such outbreak occurred in 1968 among schoolchildren in Norwalk, Ohio. 1 The prototype strain was identified four years later, in 1972, and was the first virus identified that specifically caused gastroenteritis in humans. Id. At S255. Other discoveries followed, with each strain named based on the location of its discovery-location, e.g., Montgomery County, Snow Mountain, Mexico, Hawaii, Parmatta, Taunton, and Toronto viruses. A study published in 1977 found that the Toronto virus was the second most common cause of gastroenteritis in children. 2
Eventually this confusing nomenclature was resolved, first in favor of calling each of the strains a Norwalk-like virus, and then simply, a norovirus ñ the term used today.
Noroviruses are estimated to cause 23 million cases of acute gastroenteritis in the United States per year, and are the leading cause of gastroenteritis in the United States.3 Of viruses, only the common cold is reported more often than viral gastroenteritis (norovirus). 4
The norovirus is transmitted primarily through the fecal-oral route and fewer than 100 norovirus particles are said to be needed to cause infection.5 Transmission thus occurs either person-to-person or through contamination of food or water. Foodborne norovirus transmission often occurs when food is contaminated by an infected food handler.6 The virus is shed in large numbers in the vomit and stool of infected individuals, most commonly while they are ill. Some individuals may, however, continue to shed the norovirus long after they have recovered from the illness.7 Aerosolized vomit has also been impacted as a mode of norovirus transmission.8
In short, and as noted by the CDC in its Final Trip Report, ì[n]oroviruses can cause extended outbreaks because of their high infectivity, persistence in the environment, resistance to common disinfectants, and difficulty in controlling their transmission through routine sanitary measures.î 5