Norovirus
Noroviruses (formerly called Norwalk virus or Norwalk-like viruses) are estimated to cause 23 million cases of acute gastroenteritis (commonly called the “stomach flu” or the “24-hour 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.
Transmission of norovirus occurs primarily through the fecal-oral route, and fewer than 100 norovirus particles are said to be needed to cause infection. 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 worker.
A large amount of norovirus is shed in the vomit and stool of infected individuals, most commonly while they are ill. Some individuals may continue to shed norovirus up to two weeks after they have recovered from the illness.
Symptoms of Norovirus infection
Usual symptoms of norovirus infection include nausea, vomiting, diarrhea, and abdominal pain. Headache and low-grade fever may also accompany this infection. The illness is usually mild and brief. It typically develops 24 to 48 hours after exposure and usually lasts for 24 to 60 hours. Recovery usually occurs in two to three days without serious or long-term health effects; however, dehydration is a concern, and some individuals may require intravenous rehydration therapy or other treatment. Immunity is not permanent and re-infection can occur.
Detection and treatment of Norovirus infection
Laboratory diagnosis is difficult. Diagnosis is often based on the combination of symptoms, particularly the prominence of vomiting, mild fever, and the short duration of illness. Actual proof of infection requires research laboratory techniques in which norovirus particles are identified by electron microscopy from samples of stool or vomit.
No specific treatment is available. Persons who are severely dehydrated might need re-hydration therapy. Check with your health care provider before taking over-the-counter medications or antibiotics.
Preventing Norovirus infection
The good news about noroviruses is that they do not multiply in foods as many bacteria do. In addition, thorough cooking destroys these viruses. To avoid contracting norovirus, make sure the food you eat is cooked completely. Shellfish (oysters, clams, mussels) pose the greatest risk and any particular serving may be contaminated; there is no way to distinguish a contaminated oyster from a safe oyster. With shellfish, only complete cooking offers reliable protection.
Wash raw vegetables thoroughly before eating or preparing salads. If you are traveling in an area that appears to have polluted water, drink only boiled drinks or carbonated bottled beverages without ice.
Wash hands with soap and warm water after using the toilet, before preparing or eating food, and after caring for the sick; exclude persons with gastroenteritis from the kitchen; and always dispose of sewage in a sanitary manner.
