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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 fall and winter months. Norovirus is also called “viral gastroenteritis”, “winter vomiting disease” and “the stomach flu”, although it is not caused by the influenza virus.
Noroviruses are found in the stool or vomit of infected individuals. The virus is very contagious and is spread by direct contact with an infected individual, contact with contaminated objects (e.g. door knobs), or consuming contaminated food and water. Most foodborne outbreaks occur when food is contaminated by an infected food handler, especially if they do not wash their hands after toileting or before preparing food. Ill persons should not prepare or handle food for others, even for their family. Foodborne outbreaks have been linked to eating raw shellfish, particularly oysters and clams harvested from waters contaminated by raw sewage. Drinking water and recreational water can also be contaminated by sewage and cause illness.
The illness often begins suddenly, about 24 to 48 hours after exposure. The most common symptoms include nausea, vomiting, stomach cramps or diarrhea. Fever is usually low grade or absent .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. 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 12 to 48 hours. People can infect others while symptoms are present and up to 3 days after symptoms has stopped. Some people may be contagious for as long as 2 weeks after recovery.
Infected individuals usually recover in 1 to 2 days without any serious or long-term health effects. No specific treatment is available, but infected individuals should drink plenty of fluids to prevent dehydration. Individuals who are severely dehydrated should seek medical attention. There is no vaccine or antiviral to prevent the illness. 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 :
Environmental cleaning and disinfection
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.
Call the ministry INFOline at 1-866-532-3161
(Toll-free in Ontario only)
Hours of operation : 8:30am - 5:00pm
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