Preventing the Spread of Norovirus

1. Basic Facts About Norovirus

What Is Norovirus?

Norovirus is a highly contagious virus that is responsible for gastroenteritis (inflammation of the intestines) in humans that is usually referred to as a norovirus infection. The specific virus responsible for causing illness in humans is the Norwalk virus, which is part of the Norovirus group. Norovirus is also referred to as the stomach flu or winter vomiting bug. It is responsible for a considerable number of inpatient and outpatient visits every year.

Norovirus Symptoms

Norovirus infection results in inflammation of the intestinal tract, which can result in sudden onset of severe diarrhea and vomiting. Some people also experience pain or cramps in the abdominal region, low-grade fever, muscle aches and pains, general feelings of discomfort, and nausea. In some cases extreme dehydration may result. In most people, symptoms last between one and three days, but traces of norovirus can remain in fecal deposits for up to several weeks or even months. Some carriers of the virus are asymptomatic (showing no common signs or symptoms of the pathogen) but are still contagious.1

How Contagious Is Norovirus?

As few as 18 particles of the virus are needed to spread the pathogen to another person, making it extremely contagious.2 This explains its ability to spread quickly, especially in closed environments such as schools, colleges, day-care centers, cruise ships and prisons. Individuals are most contagious when they are symptomatic and during the three days after recovery.

Norovirus Incubation Period

The incubation period refers to the time between first exposure to a virus or infection and the appearance of symptoms commonly associated with the virus. According to the Public Heath Agency of Canada (PHAC), the incubation period after exposure to norovirus is 12 to 48 hours, with the average period being around 33 hours.2

Who Is at Risk?

Everyone is at risk of norovirus, but the elderly, infants and people already experiencing acute or chronic comorbidities are at increased risk. Elderly patients in long-term care facilities are particularly at risk if a norovirus outbreak occurs due to general decreased strength and ability to fight off disease and illness. Patients with compromised immune systems, such as those undergoing chemotherapy or organ transplant, or those with a coinfection resulting from HIV, are also at increased risk. Immunosuppressed patients are unable to recover as quickly from norovirus, in some cases developing chronic symptoms that persist for weeks to years.3

How Is Norovirus Diagnosed?

A clinical diagnosis based on signs and symptoms usually determines whether a patient has norovirus. In outbreak situations, when the source of the outbreak needs to be determined, norovirus can be detected by measuring levels of viral RNA in fecal specimens from infected patients using a reverse transcription-polymerase chain reaction (RT-PCR) assay.

2. Norovirus Treatment

There is no recommended treatment for norovirus illness other than rest and hydration. Antibiotics are not effective, as norovirus is not a bacterium. Recovery time depends on the strength of the patient’s immune system, but for most healthy adults the virus will finish running its course within a few days. It is important to recover the liquids lost during this period due to the dehydration caused by diarrhea and vomiting. In patients unable to sufficiently replace their levels of hydration by drinking liquids, intravenous fluid rehydration might be required.

3. The Burden of Norovirus

About 300–400 outbreaks of norovirus are reported to the National Enteric Surveillance Program at the Public Health Agency of Canada each year. Only the common cold occurs more often.

Outbreaks occur more frequently during the fall and winter months. Many outbreaks go unreported. The Public Health Agency of Canada expects to see an increase in reports of norovirus outbreaks because these outbreaks were made nationally notifiable in 2009. This means that provinces and territories report cases of norovirus to the Public Health Agency of Canada.

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.

A national outbreak occurs when illness is linked in two or more provinces or territories.2

4. How Norovirus Spreads

Norovirus is shed in the stool (feces) and vomit of infected people. Transmission usually results from the accidental ingestion of contaminated feces and vomit. This can occur in several ways:

Contact with surfaces contaminated with infected stool or vomit particles

The transmission of norovirus via inanimate objects such as shared medical equipment, computers and mobile devices puts the general public at risk. This is especially true in locations such as hospitals, nursing homes, schools, colleges and cruise ships. Transmission through contaminated surfaces also increases the risk of infection for healthcare providers who care for infected patients, and for environmental service workers and custodians who clean and disinfect during an outbreak.

Contact with contaminated food and water

This can occur in restaurants and communal eating areas where an infected worker has contaminated food and water that is then ingested by customers. Food may also be contaminated at any point, such as during its growing, processing or preparation. Foods that are commonly responsible for outbreaks include leafy greens, fresh fruits and shellfish, particularly oysters.

The Role of Surfaces in the Spread of Norovirus

Hard surfaces play a particularly important role in the transmission of norovirus. Studies have shown that the virus can persist in a dormant state on steel, wood, ceramic, plastic and glass for up to 28 days.4 The long persistence means that transmission may still occur long after a surface is contaminated. Only a small amount of the highly contagious virus needs to be transmitted to cause an infection.

The rapid spread of norovirus was shown by the results of a study that assessed the ability of hands and cloths to spread norovirus-contaminated fecal material to other hand-contact surfaces, such as faucets, door handles and phones.5 The study showed that contaminated hands could transfer the virus to up to seven otherwise clean surfaces that hands often touch. Another study used a harmless surrogate virus to mimic the spread of norovirus in an office building. At the beginning of the day, the surrogate was placed on common surfaces such as doorknobs and tabletops. After several hours, the hands of 40-60% of office workers had become contaminated. Many other commonly touched surfaces were also contaminated within a short period of time.6

5. Preventing the Spread of Norovirus

Proper hygiene and safe food handling and preparation practices are key to reducing the risk of all food borne illnesses including noroviruses.

  • Wash your hands thoroughly with warm water and soap after using the washroom and before preparing food.
  • Make sure that you wash your hands thoroughly with warm water and soap after changing diapers. Dispose of dirty diapers properly.
  • If your child is sick with a norovirus, keep him or her home from daycare or school, and reduce contact with other children. Do not allow children who are ill and infants in diapers in areas where food is prepared.
  • Ensure your children wash their hands thoroughly, especially if they have persistent diarrhea. This is particularly important for children who are still in diapers.
  • Carefully wash fruits and vegetables with clean water.
  • Keep raw foods away from other foods while shopping, storing and preparing foods.
  • Avoid raw shellfish, including oysters. Cook thoroughly before eating. .
  • Make sure to thoroughly clean any vomit and/or feces with soapy water and disinfect with a bleach solution immediately after illness.
  • Immediately remove and wash clothing or linens that may be contaminated with the virus.
  • After handling foods in the kitchen, especially raw foods such as meat and fish, thoroughly clean and sanitize all surfaces used for food preparation with a kitchen sanitizer (following the directions on the container) or use a bleach solution (add 5 ml household bleach to 750 ml of water), and rinse with water.

If you think you are infected with a norovirus or any other foodborne or waterborne illness, do not prepare food for other people.7

6. Help Prevent the Spread of Norovirus with CloroxPro Products

PHAC recommends cleaning and disinfecting contaminated surfaces using an Health Canada-registered disinfectant effective against norovirus. The following Clorox Healthcare and CloroxPro products have Health Canada-approved claims against norovirus. Always follow the label’s directions for use when cleaning and disinfecting.

Product DIN no. Active ingredient Contact/wet time
Clorox Healthcare® Fuzion® Cleaner Disinfectant 02459744 Sodium hypochlorite 1 min
Clorox Healthcare® Bleach Germicidal wipes 02465671 Sodium hypochlorite 1 min
Clorox Healthcare® Bleach Germicidal Disinfecting Cleaner 02469278 Sodium hypochlorite 1 min
Clorox® Clean-Up® Disinfectant Bleach Cleaner 02494019 Sodium hypochlorite 1 min
Clorox® Germicidal Bleach 02459108 Sodium hypochlorite 5 min
Clorox Healthcare® Hydrogen Peroxide Cleaner Disinfectant Wipes 02406225 Hydrogen peroxide 3 min
Clorox Healthcare® Hydrogen Peroxide Cleaner Disinfectant 02403528 Hydrogen peroxide 1 min
Clorox® Total 360® Disinfectant Cleaner 02460769 Quaternary ammonium chloride 2 min


1. Mayo Clinic. Norovirus infection. January 31, 2017. Accessed January 3, 2018.
2. Public Health Agency of Canada. Norovirus Fact Sheet.,days%20after%20they%20have%20recovered.. Accessed August 17, 2020.
3. Bok K, Green KY. Norovirus gastroenteritis in immunocompromised patients. N Engl J Med. 2012;367(22):2126-2132. doi: 10.1056/NEJMra1207742
4. Kim AN, Park SY, Bae SC, Oh MH, Ha SD. Survival of norovirus surrogate on various food-contact surfaces. Food Environ Virol. 2014;6(3):182-188.
5. Barker, J, Vipond IB, Bloomfield SF. Effects of cleaning and disinfection in reducing the spread of Norovirus contamination via environmental surfaces. J Hosp Infect. 2004;58(1):42-49.
6. Gerba CA. How quickly viruses can contaminate buildings — from just a single doorknob. American Society for Microbiology’s 54th Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC), 2014.
7. Melinda Wenner Moyer. “How to Prevent Nasty Stomach Bugs This Winter? More Bleach.” New York Times 29 Nov 2018.