• “Raw oyster" in this brief review of risks refers to oyster intended for raw consumption;
• Raw oysters are considered high-risk food as pathogenic microorganisms may accumulate in their internal tissues during filter feeding;
• Hygiene measures such as reliable source of supply, temperature and time control, and prevention of cross-contamination should be ensured in the process of raw oyster production and operation;
• Cooking oysters thoroughly is the most effective way to minimise the risk of food poisoning caused by pathogenic microorganisms;
• Young children, the elderly, pregnant women and immunocompromised persons should avoid consuming raw oysters;
• The sector should clearly inform customers of the source and species of raw oysters they supply.

Introduction

       In the past three months, through the food incident surveillance system, the Municipal Affairs Bureau (IAM) has learnt that there have been several food safety incidents in Europe and America involving raw oysters contaminated with norovirus, resulting in large-scale food recalls in many countries and regions. In February 2024, food safety authorities in a neighbouring region investigated two cases of food poisoning linked to raw oysters, and pointed out that raw oysters are high-risk food and should be avoided by pregnant women, young children, the elderly and immunocompromised persons. These food safety incidents showed that the microbiological risks associated with the consumption of raw oysters cannot be ignored.

Raw Oysters Are High-risk Food

       Oysters are bivalve molluscs. They are generally grown or cultured in coastal waters and feed by filtering plankton from seawater. Therefore, maintaining good water quality in oyster growing bays helps to ensure the safety and quality of the oysters. However, human activities have inevitably affected the quality of coastal waters. For example, when oysters live in polluted waters, pathogenic microorganisms such as norovirus, hepatitis A virus, Vibrio parahaemolyticus, and Vibrio vulnificus can accumulate in their internal tissues during filter feeding. There is therefore an inherent risk in eating raw or undercooked oysters.

Effective Measures to Reduce Microbiological Risks from Raw Oysters

       To control the microbiological hazards of oysters at source, the sector and local authorities will regularly monitor the microbiological content of oysters and the water bodies where oysters are bred and raised. Only oysters harvested in qualified production areas and meeting food safety and hygiene standards can be supplied for direct human consumption.

      In addition to ensuring a secure source of oysters, hygiene measures such as temperature and time control and prevention of cross-contamination during subsequent transport, reception, storage, handling and supply processes are of paramount importance. Throughout the production and operation processes, raw oysters must be stored in a controlled, uninterrupted cold chain and the time between harvesting and serving should be minimised; specialised equipment and utensils should be used for the storage and handling of raw oysters, and raw oysters should not be re-immersed in water to avoid cross-contamination. In addition, the sector should clearly inform customers of the source and species of raw oysters they supply, so that in case of food poisoning, the public can provide relevant information to their doctors and the competent authorities to facilitate investigations.

       In fact, cooking oysters thoroughly is the most effective way to minimise the risk of food poisoning caused by pathogenic microorganisms. Cooking to an internal temperature of 90°C for 90 seconds effectively kills pathogenic microorganisms in oysters.

Regulatory Situation in Macao

       According to the relevant laws and regulations of Macao, imported oysters are required to be declared to the competent authorities and subject to the IAM's mandatory inspection and quarantine. Importers are also required to submit valid health certificates issued by the competent authorities of the source country/region (place of origin).

      Moreover, IAM has been monitoring the safety of food on the local market through routine food surveillance, seasonal food surveillance, targeted food surveillance and the food incident surveillance system. Immediate actions are taken in accordance with the level and scope of risk to control the spread of the risk. Apart from issuing food alerts to the relevant importers and retailers and instructing the recall of all problematic food products in Macao, IAM also disseminates food safety information to the public and the sector in a timely manner to ensure food safety in Macao. In addition, IAM has issued the “Hygiene Guidelines for Handling Raw Oysters" to remind the sector of the food hygiene and safety matters to be observed in the purchase, storage, handling and display of raw oysters.

Advice to the Food Industry and the Public

• Raw oysters should be purchased from reputable businesses with good hygiene conditions, and the place of origin of the oysters should be clearly known to ensure that they have valid health certificates issued by the competent authorities of the source country/region (place of origin);
• The food industry should adopt strict hygiene control measures (including but not limited to):
• Using a cold chain throughout the transportation process for temperature control;
• Use specialised equipment and utensils for the storage and handling of raw oysters; avoid re-immersing raw oysters in water to avoid cross-contamination;
• Apply the “first in, first out" principle and serve or use raw oysters with an earlier harvesting date as shown on the health certificate first, so as to minimise the time between harvesting and consumption.
• Do not eat uncooked oysters that are intended for consumption after cooking;
• Although some manufacturers are technically capable of manufacturing pre-packaged frozen oysters for raw consumption that comply with food safety and hygiene standards, these products are still considered high-risk food;
• Raw oysters are high-risk food and young children, the elderly, pregnant women and immunocompromised persons should avoid eating raw oysters;
• Cooking oysters thoroughly is the most effective way to minimise the risk of food poisoning caused by pathogenic microorganisms. The microorganisms in raw oysters cannot be killed by mustard, lemon juice or alcohol;
• The public are advised to maintain a balanced diet and avoid excessive consumption of raw oysters and to seek medical attention immediately if they feel unwell after eating raw oysters.

References:

1. Minimising Health Risk on Oyster Consumption (Hong Kong Centre for Food Safety), December 2023
    https://www.cfs.gov.hk/tc_chi/multimedia/multimedia_pub/multimedia_pub_fsf_209_01.html

2. Is Wet Storage of Imported Raw Oysters Appropriate? (Hong Kong Centre for Food Safety), November 2021
    https://www.cfs.gov.hk/tc_chi/multimedia/multimedia_pub/multimedia_pub_fsf_184_01.html

3. “Purified Oysters” Are Not Absolutely Safe and Should Not Be Consumed Raw (Baoding Administration for Market Regulation), September 2019
    https://scjgj.baoding.gov.cn/ygzw/view_961.html

BRR 001 DAR 2024