Summary

• Norovirus infections are more common in the winter and spring seasons, while cases of foodborne norovirus infections have been recently reported in neighbouring regions;
• Norovirus can be transmitted through consumption of contaminated food or water, contact with an infected person's vomitus or faeces, contact with contaminated objects, or via respiratory droplets;
• To prevent foodborne diseases, the food sector and the general public ought to thoroughly wash fruits and vegetables;
• Cook food thoroughly, especially high-risk foods such as shellfish, which are prone to contamination by norovirus;
• Maintain good personal hygiene;
• Wash hands correctly before handling food, after using the toilet, and after handling garbage;
• If symptoms such as diarrhoea, vomiting, or fever occur, refrain from handling and processing food immediately, and report to the person in charge of the food premises at once. Employ effective disinfection measures if the premises is suspected to have been exposed to contamination.

Introduction

        Norovirus infections are more common in the winter and spring seasons, while cases of foodborne norovirus infections have been recently reported in neighbouring regions. Norovirus can be transmitted through the consumption of contaminated food or water, and contact with an infected person or contaminated objects, among others. This Brief Review gives an overview of the transmission routes of norovirus, offering the general public and the food sector with advice and reminding them of the precautions to be taken with respect to personal, environmental, and food hygiene in order to reduce risk of outbreaks of foodborne gastroenteritis caused by norovirus and ensure food safety.

Norovirus, its transmission routes and preventive and control measures

       Norovirus infections are more common in the winter and spring seasons and norovirus is the leading cause of non-bacterial acute gastroenteritis, and is one of the common causes of food poisoning. Symptoms of norovirus infection include nausea, vomiting, diarrhoea, abdominal pain, and mild fever. Norovirus can be transmitted through the consumption of contaminated food or water, contact with an infected person's vomitus or faeces, contact with contaminated objects, or via respiratory droplets. The symptoms of norovirus infection in young children, the elderly, pregnant women, and individuals with a compromised immune system can be more severe.

Foodborne transmission

        Norovirus infections may originate from food contaminated at source, including oysters harvested from contaminated waters, or fruits and vegetables irrigated with contaminated water. Common infections are often associated with consumption of undercooked shellfish (e.g. raw oysters). If the oyster is contaminated with norovirus, dipping it in lemon juice or vinegar when eating it raw cannot prevent norovirus infection. Moreover, norovirus can survive at low temperatures and is relatively heat-resistant, surviving between 0°C and 60°C. As such, foods (especially shellfish) should be thoroughly cooked to destroy norovirus.

Transmission through contact with an infected person or contaminated objects

        Norovirus is highly contagious, with as few as ten viral particles can be sufficient to causing infection. If a food handler is infected with norovirus, he or she may transmit the virus to food surfaces while handling food. Any ready-to-eat food or food that does not require reheating before consumption may become contaminated with norovirus. Consumption of norovirus-contaminated food can trigger large-scale outbreaks of foodborne disease, posing a threat to public health. As such, food handlers who are infected or suspected of being infected with norovirus should immediately refrain from handling and processing food, and report to the person in charge of the premises at once. They should not return to work until at least 48 hours after the symptoms have ceased.

        Furthermore, if food handling areas (e.g. countertops), food utensils, and other objects that come into contact with food are suspected of being contaminated with norovirus, effective disinfection measures should be taken. For instance, remove food residues in food utensils and food processing tools, boil them in water for 30 minutes or immerse them in a chlorine disinfectant solution, with an effective concentration of 500mg/L, for 30 minutes, and then rinsed them with clean water to prevent transmission of the virus. It is important to note that alcohol-based disinfectants are ineffective against norovirus. ⁽¹⁾

Regulatory aspects in Macao

       In accordance with current laws and regulations of Macao, all fresh and live foods (including shellfish and vegetables) must undergo mandatory sanitary and hygiene inspection upon importation into Macao to ensure the safety of foodstuffs sold in the market. Meanwhile, the Municipal Affairs Bureau (IAM) monitors, on a constant basis, information on food safety from around the world and on food recalls issued by governments worldwide, so that appropriate preventive measures can be taken promptly, as necessary, to prevent any problematic food from entering the local market.

       Moreover, IAM has uploaded “Guidelines on Personal Hygiene for Food Handlers", “Hygiene Guidelines on Cleaning and Disinfection/Sterilisation of Food and Beverage Utensils" and “Hygiene Guidelines for Handling Oysters", among others, to remind the food sector of the personal, environmental, and food hygiene and food safety practices to take note of during production and operation. For more details, please refer to section of “Trade Information – Trade Guidelines" on the website of “Food Safety Information".

Advice to food sector

• ​Purchase food ingredients from reliable suppliers, find out the place of origin of the ingredients and obtain other necessary information before purchase, and retain invoices of delivered food products and sales records;
• Store raw and cooked foods separately, and use different utensils to handle raw and cooked foods, and raw and ready-to-eat foods, to avoid cross-contamination;
• During the production and commercialisation of raw oysters, ensure reliable source of supply, adequate temperature and time control, and necessary hygiene measures are in place to avoid cross-contamination;
• Pay attention to the cooking time and cooking temperature of food to ensure food is thoroughly cooked, especially for shellfish;
• Wash hands correctly before handling food, after using the toilet, and after handling garbage. Use utensils such as tongs, chopsticks, and spoons to minimise direct hand contact with food (especially ready-to-eat food products);
• In case of gastrointestinal disturbances, refrain from handling and processing food;
• Dispose of food that might be contaminated with norovirus;
• Pay attention to food alerts and announcements released by the Department of Food Safety of IAM. When notified of a halt of sales or a food recall by the Department of Food Safety, the food sector has to immediately halt the sale and supply of the suspected contaminated food products and cooperate with the Department of Food Safety to carry out food recall and related actions.

Advice to members of the public

• Do not buy oysters, intended to be eaten cooked, for raw consumption;
• Maintain a balanced diet and avoid consumption of oysters in excess;
• While shopping for ready-to-eat fresh vegetables, carefully check for spoilage, mould growth, and other signs of deterioration. Thoroughly wash the vegetables or immerse them in clean water before consumption;
• If there are concerns about the hygiene and quality of any food, do not consume it;
• High-risk individuals such as the elderly, young children, and those with a comprised immune system should avoid consuming seafood, vegetables, and their products which are not thoroughly cooked.

References:

1. Notice from the General Office of the National Disease Control and Prevention Administration on the issuance of technical guidelines on prevention, control and disinfection against norovirus infection in schools and prioritised venues. (General Office of the National Disease Control and Prevention Administration) 30 November, 2024

https://www.gov.cn/zhengce/zhengceku/202411/content_6990355.htm

2. Norovirus Outbreaks (U.S. Centers for Disease Control and Prevention) 2 January 2025

https://www.cdc.gov/norovirus/outbreak-basics/index.html

3. Raw Oysters and Norovirus (Centre for Food Safety, Hong Kong) June 2021

https://www.cfs.gov.hk/tc_chi/multimedia/multimedia_pub/files/trade_202102.pdf

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BRR 001 DAR 2025