Summary

• ​Vibrio vulnificus is a pathogenic microorganism naturally found in warm seawaters. It is primarily transmitted through exposure of wounds to seawater or consumption of contaminated seafood, leading to severe infections or even death;
• High-risk foods include raw shellfish, undercooked seafood, and ready-to-eat seafood. Improper processing and storage significantly increase risk of Vibrio vulnificus infection;
• The food sector should strengthen management at the source, practice low-temperature storage and transportation, standardise processing procedures, and carry out food safety education and training, while improving labeling of risks;
• Members of the public should adopt adequate protective measures when handling seafood. Cook the seafood thoroughly before consumption and avoid eating raw seafood, while individuals of high-risk groups should exercise extra caution.

Introduction

       In recent years, cases of Vibrio vulnificus infection have occurred repeatedly around the world. The Municipal Affairs Bureau (IAM) has also identified multiple cases of Vibrio vulnificus infections resulting from contact with seafood or seawater during its routine monitoring, with some cases showing severe symptoms and even deaths. Vibrio vulnificus is a halophilic pathogenic microorganism that proliferates abundantly in warm seasons and tends to accumulate in seafood such as shellfish. Given that it is neither cold-tolerant nor heat-resistant, the storage of seafood at low temperatures and thorough cooking of seafood can significantly reduce the risk of Vibrio vulnificus infection.

Contamination sources and modes of transmission of Vibrio vulnificus

• Contamination sources
• Seafood: filter-feeding shellfish (e.g. oysters and other bivalves) that feed on food particles filtered from the water and are prone to bioaccumulation of bacteria in their body; raw or undercooked fish, shrimp and crabs; and contaminated ready-to-eat products, like sashimi.
• From water to table: eutrophication of water bodies in aquaculture*; contamination from processing equipment; improper temperature control during storage; cross-contamination between raw and cooked foods (e.g. cutting boards and knives).
• Modes of transmission
• Wound infection: after the wound comes into contact with seawater or seafood, the microorganisms enter the human body through the damaged part of the skin.
• ​​Foodborne infection: foodborne infection is directly associated with consumption of raw contaminated seafood.

*The eutrophication of water bodies in aquaculture refers to the excessive accumulation of nutrients, such as nitrogen and phosphorus, in the water bodies, leading to the proliferation of algae and other planktonic organisms. This results in deterioration of water quality and ecological imbalance (e.g. death of fish and increase in diseases).

Health risks of Vibrio vulnificus

• Wound infection: Wound infections can be mild but may lead to necrotising fasciitis, characterised by severe pain, redness, swelling and rapid tissue necrosis. Patients with necrotising fasciitis may require amputation to save their lives, and about 20% to 30% of the patients die from necrotising fasciitis.
• Foodborne infection: Foodborne infection can cause diarrhea, vomiting and abdominal pain, but usually without severe symptoms. However, if the infected person has other chronic diseases, especially liver disease and diabetes, the person may develop sepsis, with symptoms of fever, chills, low blood pressure, and blisters on the skin, which can be fatal in severe cases.

Prevention, control and risk management of Vibrio vulnificus infection

       Vibrio vulnificus is primarily transmitted through exposure of wounds to seawater or consumption of contaminated seafood. As to effectively minimise the risk of infection with Vibrio vulnificus, risk management must be in place all the way “from water to table". Currently, the measures adopted internationally are focused on these three aspects:

1. Control at the source: Regular monitoring of water quality and seafood in fishing areas, and adoption of measures to control microbiological hazards, to reduce risk of contamination at the source.
2. Procedural Control: Strict control over temperature and hygiene conditions during processing, and employ programmed procedures (e.g. rapid cooling and food irradiation) on high-risk foods like oysters, to lower the survival rate of Vibrio vulnificus.
3. End-point protection: Strengthening risk communication related to raw seafood, clearly identifying potential health risks of raw seafood, and raising public's awareness of health risk prevention.

       In recent years, IAM has identified multiple cases of Vibrio vulnificus infections in Macao and in neighbouring regions resulting from contact with seafood or seawater during its routine monitoring. In response, it has compiled guidelines such as “Hygiene Guidelines on Imported Food", “Guidelines on Personal Hygiene of Food Handlers" and “Hygiene Guidelines on Prevention of Cross-contamination" to strengthen food sector's capacity in control at the source, adoption of food safety practices, and safety management in various processing stages. It carries out promotion and education on food safety on a continuous basis, and would step up the monitoring of the safety of seafood in high-risk seasons, as necessary.

Advice to the food sector

• Control at the source: Choose seafood from unpolluted waters, retain receipts and invoices, and develop an effective traceability system.
• Procedural control: Monitor variations in temperature, ensure the storage and transportation process of seafood is maintained at a low temperature (below 4°C), handle raw and cooked foods in a different food-handling area, and disinfect equipment regularly.
  
• Safety practices: Improve employees' awareness of food safety, wear gloves when handling seafood, step up cleaning and disinfection of the food establishment, and avoid cross-contamination between raw and cooked foods (e.g. cutting boards and knives).
• Labeling and warnings: Label or indicate that seafood “must be thoroughly cooked" and warn individuals of high-risk groups (such as those with liver disease, diabetes, or compromised immune systems) about the risks of consumption of raw seafood.

Advice to the public

• Be cautious in purchase: Choose seafood that appears fresh, with intact shell, and without an unusual smell.
• Risk prevention and control: Wear gloves when handling seafood, and avoid exposure of wounds to seawater and seafood.
• Thorough heating: Cook seafood thoroughly (until the internal temperature reaches 90°C), and avoid consumption of raw seafood.
• Seek prompt medical attention: Seek immediate medical attention if symptoms such as skin redness, swelling, pain and suppuration occur.

References:

1. CXC 52-2003 “Code of Practice for Fish and Fishery Products" (Codex Alimentarius).

2. “Guide for the Control of Molluscan Shellfish" (Food and Drug Administration). 2023 Revision.

3. “Fish and Fishery Products Hazards and Controls Guidance" (Food and Drug Administration). June 2022 Edition.

4. Severe Vibrio vulnificus Infections in the United States associated with Warming Coastal Waters (CDC). 1 Sept 2023

5. Impact of Vibrio vulnificus on aquaculture and its pathogenic mechanism (Northern Chinese Fisheries). Chapter 43, Issue 6. December 2024

6. Research progress on virulence mechanism and treatment of Vibrio vulnificus (Zhejiang Medicine). Volume 47, Issue 3. 2025

7. Trade Guidelines (Department of Food Safety of IAM). 19 May 2025

https://www.iam.gov.mo/foodsafety/e/tradeguidelines/listwithtab

8. Vibrio vulnificus in food (Centre for Food Safety of HKSAR), 8 October 2018

https://www.cfs.gov.hk/english/multimedia/multimedia_pub/multimedia_pub_fsf_72_01.html

BRR 005 DAR 2025