Health authorities in Hong Kong are alerting the public to a significant outbreak of gastrointestinal illness, with Norovirus infections surging, overwhelmingly linked to the consumption of raw oysters. The Centre for Health Protection (CHP) recently confirmed that over 100 individuals contracted the highly contagious virus within less than a month, prompting strong public health warnings, especially as the Lunar New Year holiday approaches, a peak period for dining and seafood consumption.
From January 18 to February 12, the CHP recorded 45 cluster cases of food poisoning, involving a total of 135 people. Notably, 87% of these cases—39 clusters impacting 113 individuals—were definitively identified as Norovirus infections. Epidemiological investigations conducted by CHP Director Dr. Shirley Siu found that every single affected person in these specific Norovirus clusters had reported eating raw oysters during their incubation period.
Experts Urge Public to Avoid Raw Oysters
The sharp increase in cases has led to definitive warnings from academic experts. Professor Yuen Kwok-yung, a top microbiologist from the University of Hong Kong, issued a grave caution against consuming raw oysters, particularly during the winter months when the virus is more persistent in the environment.
Professor Yuen explained that oysters, as filter feeders, concentrate contaminants from seawater, capable of accumulating Norovirus at levels up to 99 times higher than the surrounding water. He stated that raw oysters are the source for approximately 90% of Norovirus outbreaks. Furthermore, since the virus is highly temperature-resistant and cannot be killed by alcohol-based sanitizers, thorough cooking is the only reliable method of prevention. “I only eat oysters that have been thoroughly boiled,” Professor Yuen emphasized.
The health implications of severe Norovirus infection extend beyond typical gastrointestinal distress. Rapid, severe dehydration caused by vomiting and diarrhea can thicken the blood, posing a risk of precipitating serious cardiovascular events such as heart attacks or strokes, especially in the elderly and those with chronic diseases.
Cluster Outbreaks Lead to Supply Chain Action
In addition to earlier incidents, a recent cluster was identified at the O DELICE! restaurant branch located in THE ONE shopping mall in Tsim Sha Tsui. Seven patrons, aged between 24 and 45, developed symptoms including diarrhea, vomiting, and fever after consuming raw oysters during late January and early February.
The Food and Environmental Hygiene Department swiftly tracked the source of the implicated oysters to two suppliers, “Gate One International Food” and “88 Investment Holdings Limited.” Both companies have been immediately ordered to halt the sale of the contaminated product pending further investigation, underscoring the prompt response mandated by Hong Kong’s food safety protocols.
High Contagion Risk Beyond Food
While raw shellfish is the primary vehicle for this current outbreak, experts caution that Norovirus is notoriously contagious and transmits easily through person-to-person contact and environmental surfaces.
Taiwanese specialist Dr. Huang Hsuan added that the virus typically has an incubation period of 10 to 50 hours, resulting in harsh symptoms like explosive vomiting, severe watery diarrhea (4 to 8 times daily), and low-grade fever. For young children, severe vomiting can quickly lead to metabolic acidosis. Immediate medical attention is vital if patients experience:
- Continuous vomiting exceeding 12 hours.
- Blood in stool.
- Altered consciousness.
Norovirus is challenging to contain because it remains viable on surfaces and resists ordinary disinfectants. Zhang Xiang, a researcher at Nanjing’s Jiangsu Provincial People’s Hospital, confirmed scientific evidence supporting the risk of aerosol transmission—meaning the virus can potentially spread via aerosolized particles, particularly in poorly ventilated public restrooms. However, health officials stress that this is not the main route and the general risk remains low compared to foodborne or direct contact transmission.
Prevention and Next Steps
To mitigate the accelerating risk, particularly given the proximity of festive gatherings, the CHP advises all citizens to prioritize excellent hygiene practices. Consumers must avoid raw or undercooked shellfish entirely. Given its resistance to alcohol, the most critical self-protection measure remains the thorough washing of hands with soap and water for at least 20 seconds, especially after using the toilet and before handling food.
The authorities continue to monitor catering outlets closely and urge restaurants to ensure meticulous food preparation and strict adherence to hygiene standards to curb the spread of this potent seasonal gastrointestinal threat.