Norovirus and food

Noroviruses, the name given to a group of viruses that include the Norwalk virus, cause a mild, self-limiting gastroenteritis with symptoms of nausea, vomiting, diarrhea and abdominal pain. Noroviruses are a genus belonging to the virus family Caliciviridae and are transmitted by the fecal-oral and the aerosol routes.

Noroviruses can survive outside the host and are more resistant to common disinfectants than bacteria. Norovirus is reported to be resistant to pH as low as 2.7, heating (60 °C, 30 minutes) and free chlorine (up to 1 mg free chlorine/L, 30 minutes exposure time).

It has been widely reported on cruise ships, where it is often spread by person-to-person contact or from infected food handlers.

Raw or inadequately steamed oysters and clams are often associated with noroviruses. Symptoms generally develop twenty-four to forty-eight hours after consuming contaminated food and last twenty-four to sixty hours.

In Sweden the most implicated food in norovirus outbreaks is uncooked frozen berries, served in pastries or as a cold sauce. Indirect contamination of food via an infected food handler is more likely when the food requires extensive handling, eg salads, tarts and cold cuts.

Noroviruses are the most common cause of nonbacterial gastroenteritis, accounting for two-thirds of all illnesses caused by known food borne pathogens and for more than 90% of nonbacterial gastroenteritis in the United States.
Norovirus and food

Norwalk virus

Viruses don’t multiply in food. They only use food as a transport medium to gain entry into human body where they multiply. Norwalk and Norwalk-like viruses are the most common cause of foodborne viral illness.

Norwalk and Norwalk-like viruses have been responsible for outbreaks of gastroenteritis by victims who consume contaminated food or water. This group of virus is responsible for sporadic cases of gastroenteritis in the community and for outbreaks.

The virus can be transmitted by eating improperly cooked shellfish, such as oysters that have been gathered from waters where raw human sewage is present. Ice made from contaminated water can also be a source of infection.

This virus was initially described in 1972 and derived its name from an outbreak of acute gastroenteritis in a secondary school in Norwalk, Ohio. It was suspected but never proven that the source of infection was contaminated water supply. Illness spread by person-to-person contact within the community.
Norwalk virus