[Ask Dr Chiu] Understand the causes, transmission, symptoms, treatment, and prevention of Norovirus infection!
Health2025-03-26
6 Mins Read
Have you ever experienced a situation where you suddenly feeling nauseous, even suffering from vomiting and non-stop diarrhoea, leaving you so weak that you can barely stand up? Often, we might suspect that we've simply eaten something bad, but have you considered that the culprit might not be spoiled food, but Norovirus?
Norovirus, also known as the Norwalk virus, is an extremely contagious virus. According to the China Center for Disease Control and Prevention, the virus tends to peak from October to March of the following year. It can spread not only through contaminated food and water, but even by touching contaminated door handles or elevator buttons. What's even more troublesome is that the transmission of this virus is remarkably fast, often causing outbreaks in schools, offices or restaurants. Therefore, understanding how Norovirus spreads, its symptoms, treatment methods, and preventive measures can help protect not just yourself but also those around you. This article will provide you with a comprehensive guide to Norovirus, helping you stay safe no matter where you are!
Causes of Norovirus infection and main transmission routes
Norovirus infection typically arises from contact with contaminated food or water. The virus can also be transmitted through human excreta (such as vomit or faeces) and can reproduce rapidly in a very short period of time. Due to the strong resistance to environmental conditions of Norovirus, allowing it to survive even in extreme temperatures. It only takes a small amount of virus particles (around 10 to 100 virus particles) to cause an infection. The high contagiousness of Norovirus makes control and prevention more challenging.
Main transmission routes:
1. Contaminated food and water: Norovirus can enter the human body through contaminated food or water. Contaminated food, such as raw seafood (e.g. oysters), or tainted water, are common transmission routes.
2. Direct contact: Contact with virus-contaminated items, such as door handles, elevator buttons, or toilet facilities, followed by touching the mouth or eyes, can increase the risk of infection.
3. Person-to-Person transmission: Close contact with an infected person, particularly sharing food or drinking water, can also result in virus transmission.
4. Aerosol transmission: Although Norovirus primarily spreads through the digestive tract, in certain situations, fine droplets from vomit may be inhaled, causing infection. Therefore, if an infected person vomits in restaurants or public places, it could lead to exposure for others.
High-risk groups for Norovirus infection
The following groups are at higher health risk after contracting Norovirus:
- Infants and young children: With an underdeveloped immune system, they are more susceptible to infection and tend to experience more severe symptoms.
- Elderly: With weaker immunity, infection can lead to complications such as dehydration and electrolyte imbalances.
- Immunocompromised individuals: People with chronic illnesses, organ transplant recipients, or those undergoing chemotherapy have lower resistance to the virus and may experience longer recovery times.
- Healthcare workers and caregivers: Frequently coming into contact with patients, they are at a higher risk of infection.
- School and food service workers: Being in high-traffic environments, the chance of being exposed to the virus is higher.
Symptoms of Norovirus infection
The symptoms of Norovirus infection often appear very suddenly, and the main symptoms are similar to those of other types of gastroenteritis, but there are some characteristic signs listed below.
Main symptoms:
- Sudden vomiting: This is usually the first symptom to appear, with a rapid onset, and it is common in children and adolescents.
- Diarrhoea (Watery stool): Diarrhoea is one of the common symptoms, typically watery stool, and may last from several hours to a few days.
- Nausea and abdominal pain: Infected individuals often feel nauseous, accompanied by discomfort or abdominal pain, which may worsen after vomiting and diarrhoea.
Other possible symptoms:
- Fever: Some infected individuals may experience a mild fever, usually around 37.8°C (100°F).
- Headache: Headaches are another common symptom, related to the body’s discomfort caused by the virus.
- Muscle aches: Muscle pain and discomfort are common symptoms of viral infections.
- Mild dehydration: Due to diarrhoea and vomiting, infected individuals may experience mild dehydration, such as dry mouth and reduced urine output, so it is important to rehydrate. If symptoms worsen and severe dehydration occurs, medical treatment may be required.
Norovirus incubation period and recovery time
The incubation period for Norovirus is typically between 12 and 48 hours, meaning symptoms usually appear about 1 to 2 days after infection. For most people, symptoms will naturally subside and gradually resolve within 24 to 72 hours, without causing long-term health problems. However, during the illness, patients need to rest appropriately and stay hydrated to prevent dehydration.
Treatment for Norovirus
Currently, there is no specific medication to directly treat Norovirus. The main goal of treatment is to alleviate symptoms and prevent dehydration.
1. Rehydration and electrolyte replacement (Prevent dehydration): Since Norovirus infection can lead to diarrhoea and vomiting, patients are at risk of dehydration. Therefore, replenishing fluids and electrolytes (such as sodium and potassium) is a key part of treatment and Oral rehydration salts (ORS) or electrolyte drinks are recommended, while sugary drinks should be avoided as they can worsen diarrhoea.
2. Dietary adjustments: Before and after recovery, it is advisable to eat light, easy-to-digest foods such as plain porridge or cooked vegetables. It is best to avoid greasy, hard-to-digest, spicy, fried, or high-fat foods as these can irritate the gastrointestinal system and slow down the recovery.
3. Symptom relief
- Adequate rest: Sufficient rest helps strengthen the immune system and aids the body in fighting the virus more effectively.
- Anti-emetic and anti-diarrhoeal medications: Some patients may take anti-nausea or anti-diarrhoea medications as advised by their doctor to alleviate discomfort caused by vomiting and diarrhoea. However, these medications should only be used under medical supervision to avoid self-medication.
4. Severe cases: For patients who experience severe dehydration, particularly the elderly, infants, or those with weakened immune systems, intravenous fluids may be necessary to quickly and effectively rehydrate and restore electrolytes, preventing complications from occurring.
How to prevent Norovirus infection
Preventing Norovirus infection is not complicated. By maintaining basic hygiene and health habits, you can effectively reduce the risk of infection and create a safer environment for yourself and others.
1. Good personal hygiene habits: Regular handwashing is one of the simplest and most effective ways to prevent Norovirus. Wash your hands with soap for at least 20 seconds before eating, after using the toilet, and after touching items in public places. Particularly when handling food or after contacting others, keeping your hands clean is essential. If water is not available, using an alcohol-based hand sanitiser is also a good option.
2. Food and water safety: Avoid consuming improperly handled food, especially raw or undercooked seafood (such as oysters), which is prone to contamination by Norovirus. Ensure proper hygiene during food preparation and be mindful of the safety of drinking water, choosing treated or clean sources to avoid potential foodborne transmission.
3. Environmental cleanliness and disinfection: Maintain a clean living and working environment with good ventilation, especially in areas prone to contamination, such as kitchens and bathrooms. For areas that may have been exposed to Norovirus, use diluted bleach or disinfectant cleaners for thorough cleaning. Patients who share a bathroom should also disinfect it after each use, helping to eliminate the virus and reduce the risk of cross-contamination.
4. Avoid close contact with infected individuals: If a family member or colleague is infected with Norovirus, avoid close contact with them. Additionally, the virus is highly concentrated in their vomit and faeces, so care should be taken when handling potentially contaminated items.
5. Boosting immunity: Maintaining a healthy lifestyle helps strengthen your immune system, thereby reducing the risk of infection. A balanced diet, adequate sleep, and regular exercise can support overall health, making your immune system more resilient against viral attacks.
1. Centre for Health Protection (2025). Norovirus. Available at: https://www.chp.gov.hk/en/healthtopics/content/24/33.html
2. Platts-Mills, J.A., Taniuchi, M., Uddin, M.J., Sobuz, S.U., Mahfuz, M., Gaffar, S.A., Mondal, D., Hossain, M.I., Islam, M.M., Ahmed, A.S. and Petri, W.A., 2017. 'Association between enteropathogens and malnutrition in children aged 6–23 mo in Bangladesh: a case-control study'. The American Journal of Clinical Nutrition, 105(5), pp.1132-1138.
3. Liu, P., et al., 2021. 'Advances in the study of norovirus infection and its prevention'. Frontiers in Microbiology, 12, p.648.
4. Zheng, D., et al., 2020. 'Norovirus infection: Epidemiology, pathogenesis and clinical management'. Frontiers in Pediatrics, 8, pp.1-9. 5. Khamrin, P., et al., 2020. 'Norovirus infection in children with acute gastroenteritis in Japan: A 10-year retrospective study'. Journal of Clinical Virology, 129, p.104539.
6. Santos, N., et al., 2021. 'Norovirus: Epidemiology, clinical manifestations, and diagnosis'. Journal of Clinical Microbiology, 59(3), pp.e02218-20.
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