Norovirus is a highly contagious infection also known as Norwalk virus. It is a common cause of vomiting and diarrhea each winter and is often referred to as ‘winter vomiting disease’ or ‘stomach flu’ (although it is not caused by the influenza virus). Norovirus infections have been linked to outbreaks of vomiting and/or diarrhea in child care centres and schools, long-term care and retirement homes, cruise ships, camps, restaurants, households and other places where people gather.

Norovirus spreads easily, and commonly within the household of a person sick with the virus.

Norovirus is found in the stool and sometimes in the vomit of a person sick with the virus. People can become infected with the virus in several ways:

  • Direct contact with an ill person (e.g. shaking hands)
  • Touching surfaces or objects contaminated with the virus (e.g. doorknob or stair railings) and then touching your mouth or eyes
  • Eating food or drinking beverages that have been contaminated by an ill person
  • Eating food such as raw shellfish harvested from contaminated waters (e.g. oysters and claims)
  • Airborne transmission has been suggested to explain its rapid spread in settings like schools and child care centres

Those infected with Norovirus usually spread it once they feel ill and for up to two days after the symptoms (usually diarrhea) stop but can continue to spread the virus for up to two weeks after their symptoms stop.

People infected with Norovirus usually experience sudden onset of nausea, vomiting, stomach cramps and watery diarrhea that lasts about one to three days. Other symptoms may include fever, headache, muscle aches and malaise.

Symptoms usually appear within ten hours but can develop up to two days after exposure to the virus. Infected individuals usually recover in two to three days without serious or long-term health effects.

Severe illness or hospitalization is uncommon. Dehydration is the most common complication, especially among young children and the elderly.

Seek medical attention or call Health Connect Ontario (8-1-1) to talk to a registered nurse if you have high fever, bloody diarrhea or illness lasting longer than 72 hours.

Doctors generally diagnose Norovirus infection based on symptoms including the sudden onset, the short duration (usually one to three days) and the quick resolution of the infection. However, a stool sample may be collected by your doctor in certain circumstances.

People sometimes call Norovirus infection the “stomach flu.” However, influenza (the flu) is a respiratory (lung) illness with symptoms of cough, sore throat and fever. Getting your flu vaccine each fall/winter, while important for protection against the flu, will not protect you against Norovirus infection.

  • Keep your hands clean. Wash your hands often with soap and warm water for at least 15 seconds after using the toilet, diapering a child and before preparing or eating food. This is the best way of reducing the risk of getting infected with Norovirus.
  • If soap and water are not available, and if hands are not visibly soiled, use an alcohol-based hand sanitizer with 70% – 90% alcohol.
  • Thoroughly and frequently clean and disinfect environmental surfaces and equipment with a chlorine bleach disinfectant, especially in areas that are touched often (e.g., telephones, door handles, gym equipment, bed side rails, etc.). A chlorine bleach solution of one part household bleach to 49 parts water can be made from two teaspoons of household bleach mixed with two cups of water.
  • Avoid raw shellfish, including oysters and clams. Cook all shellfish thoroughly before eating.

There currently is no vaccine available in Canada to prevent Norovirus infection.

Most people will recover from a Norovirus infection with no complications. The symptoms of Norovirus infection may be more severe for infants, young children, the elderly and those with weak immune systems. Dehydration can be more serious for these individuals and they should seek medical attention if this becomes severe.

  • Anyone who is ill with diarrhea or vomiting should stay home until well for at least 48 hours after symptoms stop (especially for those who work with food, the elderly or at a hospital or child care centre).
  • Do not visit hospitals, child care centres or long-term care and retirement homes until you have been well for at least 48 hours after symptoms stop.
  • Do not prepare food for others for at least 48 hours after symptoms stop.
  • It is important to stay home when you are sick to prevent the spread of infections. In addition to the recommendations above, complete Ontario’s Self-Assessment or Ontario’s School and Child Care Screening for children before returning to work or school/child care.
  • Keep your hands clean. Wash your hands often with soap and warm water for at least 15 seconds after using the toilet, changing a diaper or vomiting.
  • Drink lots of fluids to avoid dehydration.
  • Seek medical attention if symptoms become severe or last longer than 72 hours.
  • Clean and disinfect high traffic/touch areas (e.g. taps, bathrooms, doorknobs, surfaces, etc.) frequently with a diluted bleach and water solution. Some household disinfectants may not work against Norovirus. A chlorine bleach solution of one part household bleach to 49 parts water can be made from two teaspoons of household bleach mixed with two cups of water.

There is no specific treatment for Norovirus infection. Antibiotics are not useful because the illness is caused by a virus, not a bacterium. Individuals who are sick with Norovirus should drink plenty of fluids to prevent dehydration.

Norovirus infections are typically not reportable to public health. However, outbreaks of enteric illness that may be caused by norovirus that occur in institutions (such as hospitals, long term care homes or retirement homes), schools or child care centres, or other community settings are reportable. Public health plays a role in the follow up of such outbreaks to investigate cause, provide appropriate follow up to those who are affected and/or sick and ensure control measures are in place to prevent the spread of infection.