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Noroviruses Facts

This fact sheet provides information for health care workers about Noroviruses

Norovirus (formerly known as Norwalk-like viruses) infection is a gastrointestinal illness that occurs at irregular intervals or in outbreaks. The virus was first identified during a gastroenteritis outbreak in Norwalk, Ohio, in 1972. The illness only occurs in humans and the virus is found worldwide. Of all viruses, only the common cold is reported more often than viral gastroenteritis. Although the illness can occur at any time, it most commonly occurs in the period from October to April. Norovirus is also called viral gastroenteritis, winter vomiting disease and the stomach flu, although it is not caused by the influenza virus.


Norovirus is spread by exposure to infected individuals or contaminated food and water. The virus is passed in stool and vomit. It is usually spread from person-to-person by direct contact with fecally contaminated hands of an ill individual or by contact with fecally contaminated objects (e.g. door knobs) and then touching your mouth. Outbreaks have been linked to eating raw shellfish, especially oysters and clams, although any food can become contaminated if handled by an ill person. Shellfish become contaminated from stool from sick food handlers (who do not wash their hands after toiletting or before preparing food) or from raw sewage dumped overboard from recreational and/or commercial boaters. Ill persons should not prepare or handle food of others, even for their family.


Although the virus is easily spread, serious illness is rare. Symptoms of Norovirus infection may be more severe for older persons, young children and those with underlying medical conditions who are more vulnerable to dehydration because of vomiting and diarrhea. The most common symptoms include nausea, vomiting, stomach cramps or diarrhea. Fever is usually low grade or absent. If diarrhea is bloody and/or accompanied by a high fever, or if the symptoms last longer than 72 hours, seek medical attention. The illness may be due to something other than Norovirus.


The incubation period is 1-2 days. People can infect others while symptoms are present and up to 2 days after diarrhea has stopped.


Infected individuals usually recover in 2 to 3 days without any serious or long-term health effects. No specific treatment is available, but individuals should get plenty of rest and need to replace lost fluids by drinking liquids. Individuals who are severely dehydrated should seek medical attention. Antibiotics, used for bacterial infections, will not be effective against this viral infection.

People frequently refer to the symptoms of Norovirus infection as the “stomach flu”. However influenza is a much more serious respiratory illness with sudden onset of cough, headache, muscle soreness, fatigue and fever. While receiving the annual influenza vaccine is important each winter and is free for all Ontario residents, the influenza vaccine will not protect you against a Norovirus infection.


Immunity to Norovirus is short and reinfection can occur after a few weeks or months. The following actions may reduce the risk of acquiring or spreading the infection :

  • Perform hand hygiene frequently, especially after toiletting and before eating or preparing food
  • Infected health care workers should not attend work for a minimum of 48 hours after symptoms such as vomiting and diarrhea have resolved
  • Patients with suspected Norovirus infection should be managed with Routine Practices with careful attention to proper hand hygiene practices. Contact precautions should be used when caring for individuals who are incontinent, during outbreaks in a facility and when caring for pediatric populations. Please refer to the Provincial Infectious Diseases Advisory Committee’s Fact Sheets on Routine Practices and Hand Hygiene
  • Individuals who experience nausea, vomiting or diarrhea should not attend school or work and should not prepare or touch food for others
  • Avoid drinking untreated water
  • Cook all shellfish thoroughly before eating.
Environmental cleaning, disinfection
  • General routine cleaning and disinfection practices should be continued daily with hospital-grade disinfectant – a hard surface disinfectant with DIN number and the following indication on the label: “for use in a health care facility”
  • In health care settings, attention must be given to high touch surfaces such as bed rails, sinks, chairs, call bells, telephones, IV lines and poles, blood pressure cuffs, door handles, wall panel controls, thermostats and keyboards
  • Processes for cleaning and disinfection should include sufficient contact time for disinfectants, appropriate strength of cleaning and disinfectant solutions, use of damp dusting, working from clean to dirty areas and eliminating the practice of dipping a cloth back into cleaning solution after use and re-using it on another surface.
Further Information

Anyone with concerns or questions should contact the institution’s Infection Prevention and Control Professional (ICP), institutional occupational health and safety department, and the local public health unit, or their own health care provider for personal health issues.

For more information
Call the ministry INFOline at 1-866-532-3161
(Toll-free in Ontario only)
TTY 1-800-387-5559
Hours of operation : 8:30am - 5:00pm
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