July 2012

What Is Norovirus Infection?

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, long-term care homes as well as on cruise ships, camps, schools, restaurants, households and other places where people gather.

How Does the Norovirus Spread?

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

  • Direct contact (e.g. shaking hands) with another person who is infected
  • Touching surfaces or objects contaminated with the virus (e.g. doorknob, hand or stair railings, etc.) and then touching your mouth or eyes
  • Eating food or drinking beverages that are contaminated by an infected person
  • Eating food such as shellfish contaminated at the source
  • Airborne transmission has been suggested to explain its rapid spread in settings like schools and day cares

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

What Are the Signs and Symptoms of Norovirus Infection?

Infected individuals usually experience sudden onset of nausea, vomiting and watery diarrhea that lasts about one to three days. Other symptoms may include fever and stomach cramps.

Severe illness or hospitalization is uncommon. Dehydration is the most common complication, especially among young children and the elderly. Seek medical attention or call TeleHealth Ontario (1-866-797-0000) if you have high fever, bloody diarrhea or illness lasting longer than 72 hours.

How Long Do Symptoms of Norovirus Infection Last?

Infected individuals usually recover in two to three days without serious or long-term health effects.

How Soon Do the Symptoms Appear After I Have Been Exposed?

Symptoms usually appear within 10 hours but can develop up to two days after exposure to the virus.

How Is Norovirus Infection Diagnosed?

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.

Is Norovirus Infection the Same as the “Flu”?

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 the influenza vaccine each fall/winter (it is free for anyone who works, attends school or lives in Ontario), while important for protection against the flu, will not protect you against Norovirus infection.

How Can I Reduce My Risk of 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.
  • Do not prepare food for others if you have symptoms of vomiting or diarrhea.
  • 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 50 parts water can be made from two teaspoons of household bleach mixed with two cups of water.
  • Anyone who is ill with diarrhea or vomiting should stay home until well for at least 48 hours (especially for those who work with food, the elderly or at a hospital).

Who Is at Risk of Getting Severe Norovirus Illness?

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 who should seek medical attention if this becomes severe.

What Should I Do If I, or a Family Member, Become Infected with Norovirus?

  • Stay at home until you are well for at least 48 hours so you are no longer infectious to others
  • Do not visit hospitals, daycares or long-term care homes until you are no longer infectious
  • Drink lots of fluids to avoid dehydration
  • Seek medical attention if symptoms persist or worsen
  • Clean and disinfect high traffic/touch areas (e.g. taps, bathrooms, doorknobs, surfaces, etc.) frequently with a dilute bleach and water solution.

Can Norovirus Infection Be Treated?

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

Is There a Vaccine for Norovirus?

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

More Information

Call Toronto Public Health at 416-338-7600 (TTY at 416-392-0658) or speak to your health care provider.