Norovirus

Norovirus is a highly contagious virus that causes an upset stomach (gastroenteritis). The main symptoms are vomiting and diarrhoea.

Norovirus can cause life-threatening illness in vulnerable individuals but most people recover without the need for medical treatment. It has been estimated that approximately half a million cases of norovirus infection occur every year in New Zealand.

General information

Norovirus is the most common cause of acute viral gastroenteritis in people. It is very easily spread and affects people of all ages. It is usually passed on through food or water that is contaminated by vomit or faecal matter (poos or stools) but can also be transmitted through close contact with an infected person. Globally, norovirus is the leading cause of foodborne illness.

Causes

The main ways norovirus is transmitted are:

• Eating contaminated food
• Drinking contaminated water
• Hand-to-mouth contact after handling a contaminated surface or object
• Close contact with a person who has a norovirus infection, eg: sharing food and cutlery
• Through the air – vomiting can create tiny particles that float in the air and carry norovirus.

The norovirus is difficult to kill. It can withstand exposure to hot and cold temperatures as well as most disinfectants.

Norovirus infection commonly occurs in closed and crowded environments, eg: hospitals, nursing homes, aged-care facilities, schools, hotels, and cruise ships. The infection of a group of people in the same place and time is called an outbreak.

There were 261 norovirus outbreaks in 2017, representing 40% of all infectious disease outbreaks reported in New Zealand.

Signs and symptoms

Signs and symptoms of norovirus infection include:

• Nausea
• Abdominal pain or cramps
• Vomiting
• Diarrhoea (loose or watery stools)
• Headache
• Generally feeling unwell
• Mild fever; chills
• Muscle aches and pain.

Symptoms, especially diarrhoea, abdominal pain, and vomiting, typically begin 24–48 hours after exposure to the virus and last 1–3 days.

Medical attention should be sought if the diarrhoea does not go away within several days, or if bloody vomit or stools, severe abdominal pain, or dehydration are experienced.

People are infectious for at least three days after recovery and in some cases for up to two weeks.

Some people with norovirus may show no signs or symptoms but are still capable of spreading the virus (contagious).

Diagnosis

Diagnosis of norovirus infection is usually based on symptoms. Infection can be confirmed by testing a stool sample for the presence of norovirus.

Treatment

There is no specific medical treatment for norovirus infection. Most people recover completely without treatment.

Recovery is dependent on the health of a person’s immune system. People with an immature or weak immune system — especially infants, the elderly, and people with an underlying disease — can become severely dehydrated and require medical attention, primarily fluid replacement.

Medications to slow diarrhoea or reduce nausea should be avoided unless otherwise instructed by a doctor. In most cases, it is better to let the body clear itself of the virus.

Use of antibiotics should be avoided because they are not effective against viruses and their inappropriate use contributes to the development of antibiotic resistance.

Home care

Drink plenty of fluids, such as plain water, over-the-counter oral hydration solutions, sports drinks, and home-made broths to help to prevent dehydration.

Drinking beverages with high sugar content, such as soft drinks and fruit juices, should be avoided as they can make diarrhoea worse.

Smaller meal portions and a bland diet (e.g. soup, noodles, rice, or crackers, bananas, grilled vegetables) may help limit vomiting.

Complications

In some people – notably infants, the elderly, and people with an existing illness – norovirus infection can cause severe dehydration, malnutrition, and possibly death.

Dehydration is the main cause of serious illness. Typical signs and symptoms of dehydration include:

• Fatigue
• Dry mouth and throat
• No tears, sunken eyes, sunken fontanelle in infants
• Lethargy, dizziness, cool hands and feet or grey cold skin
• Little or no urine passed in the previous 8 hours
• Skin that does not relax after being pinched
• Urine that is dark and smelly.

Dehydration in anyone – but especially infants and children, the elderly, and people with weakened immune systems – is a reason to contact a doctor immediately.

Prevention

To help prevent becoming infected with norovirus and spreading it once infected:

• Wash hands frequently and thoroughly with soap and water or an alcohol-based gel, especially before eating or preparing food and after using the toilet or changing a nappy
• Avoid preparing or handling food for at least 48 hours after the symptoms stop
• Avoid contact with people who have symptoms of diarrhoea and vomiting
• Avoid consuming contaminated food and water, including food that may have been prepared by someone who was sick
• Wash fruits and vegetables before eating
• Cook seafood thoroughly
• Dispose of vomit and faecal matter carefully, to avoid spreading norovirus by air
• Disinfect contaminated surfaces with a chlorine bleach solution wearing gloves
• Stay home from work and keep children away from school or day care
• Avoid traveling until several days after signs and symptoms have ended.

There is no vaccine against norovirus to help to prevent its spread.

Further information and support

For more information about norovirus, please see your GP or practice nurse, or contact:

Healthline

Free phone: 0800 611 116

Website: www.healthline.govt.nz

Plunket

Free phone: 0800 933 922

Website: www.plunket.org.nz

References

Cressey P., Lake R. (2011) Risk ranking: Estimated incidence of foodborne illness in New Zealand. Report FW11006 prepared for the New Zealand Ministry of Agriculture and Forestry. Christchurch: Institute of Environmental Science and Research (ESR) Ltd. Available from: https://www.foodsafety.govt.nz/elibrary/industry/estimates-burden-foodborne-disease-2011.pdf ESR (2018). Annual summary of outbreaks in New Zealand 2017 (Report; PDF). Wellington: Institute of Environmental Science and Research Ltd (ESR). https://surv.esr.cri.nz/PDF_surveillance/AnnualRpt/AnnualOutbreak/2017/2017OutbreakRpt.pdf

Mayo Clinic (2022). Norovirus infection (Web Page). Rochester, MN: Mayo Foundation for Medical Education and Research. https://www.mayoclinic.org/diseases-conditions/norovirus/symptoms-causes/syc-20355296 [Accessed: 13/01/23]

Ministry of Health (2020). Norovirus (vomiting and diarrhoea bugs) [Web Page]. Wellington: New Zealand Ministry of Health. http://www.health.govt.nz/your-health/conditions-and-treatments/diseases-and-illnesses/norovirus-vomiting-and-diarrhoea-bugs [Accessed: 13/01/23]

Ministry of Health (2009). Guidelines for the management of norovirus outbreaks in hospitals and elderly care institutions (Web Page). Wellington: New Zealand Ministry of Health. https://www.health.govt.nz/system/files/documents/publications/guidelines-management-norovirus_0.pdf

Kirk MD, et al. World Health Organization Estimates of the Global and Regional Disease Burden of 22 Foodborne Bacterial, Protozoal, and Viral Diseases, 2010: A Data Synthesis. PLoS Med. 2015 Dec 3;12(12):e1001921.

Kun LL, et al. A Multi-Site Study of Norovirus Molecular Epidemiology in Australia and New Zealand, 2013-2014. PLoS One. 2016; 11(4): e0145254.

Last reviewed: January 2023