Noroviruses are transmitted primarily through the fecal-oral route, and fewer than 100 norovirus particles are said to be needed to cause infection (MMWR, 2001, June 1).
Transmission occurs either person-to-person or through contamination of food or water. Foodborne norovirus transmission can occur when food is contaminated by an infected food handler (Caceres, et al., 1998; MMWR, 2001, June 1).
Noroviruses are recognized as causing over half of all foodborne illness outbreaks. A 2011 CDC report estimates that over 5,400,000 people become ill from norovirus infections each year. Almost 15,000 of these people are hospitalized and 149 die. CDC statistics show that food is the most common vehicle of transmission for noroviruses; of 232 outbreaks of norovirus between July 1997 and June 2000, 57% were foodborne, 16% were spread from person-to-person, and 3% were waterborne (CDC, 2006, August 3).
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 norovirus long after they have recovered from the illness (Patterson, 1993). Aerosolized vomit has also been implicated as a mode of norovirus transmission (Marks, et al., 2000).
As noted by the CDC in its Final Trip Report, “noroviruses 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” (MMWR, 2001, June 1).
For more information, visit About Norovirus.