Noroviruses - Fact Sheet
Noroviruses are a group of viruses that cause gastroenteritis in people. These viruses are part of a family called caliciviruses. While animals do carry other kinds of caliciviruses, they are not believed to carry noroviruses. The term norovirus was approved as the official name for this group of viruses in 2002. Previously, they were called Norwalk-like viruses. Noroviruses are commonly found throughout North America and are very infectious. Noroviruses can survive on practically any surface including door handles, sinks, railings and glassware. They occur throughout the year but are more common in winter and affect all age groups.
What causes infection with noroviruses?
People carry noroviruses, which are found in the stool or vomit of infected individuals, while they are ill and up to at least three or four days after recovery. Some people may be contagious for as long as two weeks after recovery. People are usually infected with noroviruses by direct contact with a person who is ill or has recently been ill or through indirect contact by touching surfaces contaminated with the virus, like door handles or by eating contaminated food or drinking contaminated water.
The virus is able to survive relatively high levels of chlorine and varying temperatures and can survive on hard surfaces in the environment for up to 12 hours. It has been found to survive on contaminated carpet for up to 12 days. Noroviruses are easily transmitted in environments where people are in close contact, including schools, day-care centres, long-term care facilities, healthcare facilities and cruise ships.
What are the symptoms of illness caused by noroviruses?
The symptoms of norovirus illness include nausea, vomiting, diarrhea and stomach cramps. Sometimes, people may have a low-grade fever, chills, headache, muscle aches and fatigue. The illness often begins suddenly, about 24 to 48 hours after exposure.
How long do the symptoms last?
In most healthy people, acute diarrhea and vomiting usually last eight to twelve hours, and people normally recover in 48 hours. Symptoms may last longer in some people.
How can norovirus infections be prevented?
You can reduce the risk of norovirus infections by:
- Washing hands frequently, especially after using the bathroom or changing diapers and before eating or preparing food. This is very important if you have recently been ill or if in contact with an ill person.
- Eat food that is well cooked and still hot when served.
- Wash fruits and vegetables thoroughly before eating.
- Thoroughly clean contaminated surfaces immediately after an episode of illness with hot, soapy water and then disinfect the area using a household disinfectant. Immediately remove and wash clothing or linen that may be contaminated with stool or vomit.
- Flush or discard any vomit and/or stool in the toilet and make sure that the surrounding area is kept clean.
- Avoid shaking out soiled linen and wear household gloves when handling soiled materials.
How long are people infectious?
People infected with norovirus are contagious from the moment they begin feeling ill to at least three or four days after recovery. Some people may be contagious for as long as two weeks after recovery. Good hygiene standards, including frequent hand washing, are very important during this period.
What is the treatment for norovirus infection?
There is no preventative treatment (vaccine or antiviral medication) for noroviruses and they cannot be treated with antibiotics because antibiotics fight bacteria, not viruses. However, healthy people normally recover on their own in about 48 hours.
Those suffering from illness should drink plenty of fluids to prevent dehydration - a possible serious health effect of norovirus infection. People should drink juice or water to reduce their chance of becoming dehydrated. Sports drinks are not recommended because they do not replace the nutrients and minerals lost during illness. If serious dehydration occurs, the ill person may require re-hydration in hospital.
Are noroviruses dangerous?
Generally, noroviruses cause unpleasant but self-limiting, gastrointestinal symptoms, such as diarrhea and vomiting. The risk of more severe illness, including dehydration, is likely to occur in the very young, the elderly and those with weakened immune systems.
Have people died of noroviruses in Canada?
Deaths have occurred in long-term health care facilities during norovirus outbreaks, but it is difficult to say to what extent norovirus caused death in already frail or sick people. It would be considered a contributing factor but not the cause of death.
Does the Public Health Agency keep track of noroviruses across the country?
The Agency monitors for gastrointestinal disease cases and outbreaks through national surveillance programs.
Is this year worse than past years?
We have recorded 300 to 400 outbreaks this year and this reflects increased reporting since 2002. This increase likely is partly linked to more incidents and partly linked to better reporting.
How many outbreaks do we see in Canada in a year?
At present we are receiving 300 to 400 outbreaks reported each year since 2002. This compares with less than 100 outbreaks in previous years (1998-2001). The increase is likely due partly to increased numbers of outbreaks and improved reporting.
What's the difference between a case and an outbreak?
A case refers to illness in one person whereas an outbreak refers to two or more people linked by a common exposure within a specific time frame.
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