Noroviruses are estimated to cause 23 million cases of acute gastroenteritis (commonly called the “stomach flu”) in the U.S. each year, and are the leading cause of gastroenteritis. Of viruses, only the common cold is reported more often than viral gastroenteritis (norovirus).

Noroviruses may cause more outbreaks of foodborne illness than all bacteria and parasites. They 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.

The norovirus is transmitted primarily through the fecal-oral route and fewer than 100 norovirus particles are said to be needed to cause infection. Transmission occurs either person-to-person or through contamination of food or water. Transmission can occur by touching surfaces or objects contaminated with norovirus and then placing that hand in your mouth; having direct contact with another person who is infected and showing symptoms; sharing foods or eating utensils with someone who is ill; exposure to aerosolized vomit; and consuming food contaminated by an infected food handler.