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Feature Article

COVID-19 and Salmon

When a new wave of COVID-19 emerged in Beijing in early June this year, many were surprised that the COVID-19 virus was detected on a cutting board used for salmon in a market.  The Centre for Food Safety (CFS) took immediate follow-up actions to find out more about the incident.  In this article, we will discuss the risk of acquiring the COVID-19 virus from aquatic food animals and the safety of aquatic products..

Aquatic Animals Unlikely to Be Infected

The COVID-19 virus belongs to a subset of coronaviruses that is only reported to infect mammals.  There is no scientific evidence indicating that aquatic food animals can be infected by this virus.  COVID-19 is a respiratory disease and the virus primarily targets our respiratory tracts and infects our lungs.  One of the major physiological differences between humans and finfish is that fish do not have lungs.  Fish are therefore not likely to be susceptible to the virus.

Should Consumers Sanitise Food Packaging?

Contaminated hands play a significant role in facilitating indirect contact transmission by transferring infectious viruses from one surface to another and even into one’s body.  Compared with food packaging, high-touch points such as door handles, handles of shopping trolleys and water taps pose a greater risk of infection.  The more frequently they are touched by different people, the higher the risk of contamination.  While some people may still opt to disinfect food packaging surfaces with common household disinfectants like alcohol-based wipes or sprays if needed, it is more important to wash hands thoroughly, especially before touching eyes, nose and mouth, after returning home from grocery shopping and after handling and storing purchased food products.

The invasion of a virus into cells depends on its ability of binding to a host cell to gain access and replicate.  The COVID-19 virus enters the host cell specifically through binding to ACE2, a cell receptor widely present in animals.  The binding is analogous to using a key to open a lock, which hinges on whether the 'keys' on the virus fit into a host cell's 'lock'.  The better fitting in terms of structure and binding sites, the greater the chance for the virus to gain access to the cell.  While rather similar morphologically across mammals, ACE2 in finfish is in many ways different in the protein sequence.  In this sense, it is not quite possible for the COVID-19 virus to infect cells of aquatic animals through ACE2, not to mention whether or not it is able to use the cell’s machinery after entering the cell for replication.

Safety of Raw Aquatic Products

Although aquatic food animals are unlikely to be infected by the COVID-19 virus, they, like any other object or surface, may potentially become contaminated, especially when handled by people infected with the virus.  Currently, there is no evidence suggesting that humans can be infected by the COVID-19 virus via food, including raw and undercooked aquatic products.  Members of the public are recommended to maintain personal, food and environmental hygiene at all times.  With proper food handling and sanitation, the likelihood of contamination of aquatic animals or their products with the COVID-19 virus should be very low.  The following are some practical reminders for consumers to enhance hygiene. 

In general, eating raw or undercooked aquatic products is associated with higher risks from microbiological hazards, as there is no or inadequate heat treatment to eliminate the disease-causing microorganisms present in the food.  Members of the public are recommended to cook food thoroughly to minimise the risk of foodborne illnesses.  Susceptible populations such as pregnant women, infants, young children, the elderly and people with weakened immunity should avoid consuming raw and undercooked foods

Some tips for consumers to enhance hygiene
Figure 1:  Some tips for consumers to enhance hygiene

Enhance Hygiene in Food Businesses

Preventing environmental contamination is also important in containing the spread of COVID-19.  Besides upholding food safety, food workers should enhance hygiene in the food business environment.  For example, they should refrain from working when having COVID-19 symptoms.  Moreover, high-touch points such as door handles, handles of shopping trolleys and water taps should be disinfected more frequently.  These measures are also applicable to wet markets.

Key Points to Note 

  1. Aquatic food animals are unlikely to be infected by the COVID-19 virus.  There is no evidence suggesting that humans can be infected by the virus via food.
  2. Similar to objects or surfaces, aquatic food animals and their products may potentially become contaminated with the virus.
  3. With proper food handling and sanitation, the likelihood of contamination of aquatic animals or their products with the COVID-19 virus should be very small.

Advice to the Trade 

Readers' Corner

Apples and Patulin

From April to early June 2020, the CFS announced that five samples of apple juice drinks, both locally produced and imported products, were found to contain excessive levels of patulin.  The CFS has ordered the food traders involved to stop selling and recall the products concerned.


Patulin is a mycotoxin produced by a variety of moulds such as penicillium and aspergillus.  It mainly occurs in rotten apples and their products.  Prepackaged apple juices are usually heat-treated (e.g. by pasteurisation) to prolong the shelf life of the product.  Although heat treatment can destroy the moulds present, it cannot remove patulin.  Ingesting high doses of patulin can cause nausea, gastrointestinal disturbance and vomiting in humans and damage to the liver, spleen, kidney and immune system in experimental animals.

Regulatory Control and Actions Taken by the CFS 

Currently, there is no specific legislation in Hong Kong regulating the level of patulin in food.  However, the local food law stipulates that all food for sale must be fit for human consumption.  Making reference to the Codex Alimentarius Commission (Codex) standards, the CFS adopts an action level at 50 ppb for patulin in apple juice and apple juice used as an ingredient in other beverages.  In addition, some other jurisdictions such as the Mainland, the European Commission, the United States and Canada have established standards/action levels for patulin in apple juice.

Preventive Measures

Control of patulin levels in apple juice is achievable through good practices such as the Good Manufacturing Practice (see Figure 2).  In this connection, the Codex has issued a code of practice with recommendations on the prevention of patulin contamination and the reduction of patulin levels in apple juice and apple juice used as an ingredient in other beverages.

A flowchart showing the general process of apple juice production and some key points to control the levels of patulin in apple juice
Figure 2: A flowchart showing the general process of apple juice production and some key points to control the levels of patulin in apple juice.

Since mould growth usually occurs in warm and humid environment, harvested apples should be stored under controlled conditions (e.g. kept refrigerated).  They should also be handled as gently as possible to minimise physical damage as any bruising will encourage patulin formation. 

Cutting off the mouldy parts of apples prior to pressing will not necessarily remove all the patulin present in the fruit as some patulin may have diffused into the seemingly "healthy" tissue.  Apples that are externally and/or internally damaged or mouldy should not be used for apple juice production (see Figure 3).  It has been reported that apple varieties with an open calyx (blossom end) are at a greater risk of patulin development within the core as fungi may enter the core early during the fruit's development.  Therefore, apples should be regularly examined for internal rots by cutting them open for cross-sectional examination before pressing.

Apples that are externally or internally damaged or mouldy should not be used for apple juice production
Figure 3: Apples that are externally or internally damaged or mouldy should not be used for apple juice production.

Key Points to Note 

  1. Patulin is a heat-stable toxin produced by a number of different moulds.
  2. High level of patulin may be found in apple juice made with damaged or mouldy apples.
  3. Control of patulin levels in apple juice is achievable through good practices.

Advice to the Trade

  1. Adopt good management practices by making reference to the Codex Code of Practice in apple juice production.

  2. Do not use damaged or mouldy apples for apple juice production.  Before pressing, cut the apples and check the cross sections for any damage or mould.

  3. Store apples and apple juices under proper conditions to prevent microbial development and patulin formation.

Spot Check

Undercooked Burger Steaks and Sunny-side-up Eggs

Burger steaks are commonly consumed foods in Hong Kong.  Some people prefer the taste and mouthfeel of medium rare or medium burger steaks to well-done patties.  Moreover, burger steaks are often served with sunny-side-up eggs.  Consumers may not be aware that undercooked burger steaks and sunny-side-up eggs can lead to the risk of food poisoning.

How Would You Like Your Burger Steak Cooked? 

Burger steaks should always be cooked till well done regardless of the quality, source and price of the meat.  When meat is minced to produce burger steaks, harmful bacteria such as Salmonella or pathogenic Escherichia coli (E. coli) on the surface will spread throughout the patty.  Unless burger steaks are thoroughly cooked, these bacteria can remain alive.  Therefore, ground beef should be cooked until the internal temperature reaches at least 75°C or until browned throughout with the juice running clear.

Sunny-side-up Eggs May Also Contain Salmonella 

Salmonella can contaminate eggs via the infected reproductive organs of hens during egg formation, or through eggshell penetration from contaminated faeces of hens during or after laying of eggs.  As sunny-side-up eggs are only fried on one side, Salmonella can be found in the egg. 

Undercooked Burger Steaks and Sunny-side-up Eggs May Cause Food Poisoning 

In March 2020, some members of the public suffered from food poisoning and developed symptoms of abdominal pain, vomiting, diarrhoea and fever after consuming medium well hamburger steaks and sunny-side-up eggs.  Investigation revealed that the incident was caused by undercooked beef patties and eggs. 

Advice to the Trade 

Updates on CFS

Food Safety Day 2020

The Food Safety Day is an annual signature event of the CFS with a view to strengthening collaboration among the Government, the trade and the public.  The theme for this year is "Eat Safe!  Know Your High-risk Foods".

What Is "Raw and Cold Food" ?

When "raw and cold food" is mentioned, it is sushi, sashimi or raw oysters that immediately come to most people's minds.  Actually, this is a loose description of raw or undercooked foods, generally referred to as high-risk foods.  Common food products may also contain raw or undercooked ingredients, for examples, mango pudding made with raw eggs, smoked salmon sandwiches and congee prepared with undercooked beef. 

Food Safety Day 2020 

Through Food Safety Day 2020, the CFS reminds the public to stay vigilant in handling and consuming high-risk foods in their daily diet.  This year, the CFS has produced four specific promotional leaflets to separately introduce the potential risks of consumption of "raw and cold food" by four susceptible groups (pregnant women, infants, young children, the elderly and immunocompromised persons), so that the public can practise food safety in choosing foods.  The CFS also takes the opportunity to advise the trade what efforts can be taken to enable consumers to make informed decisions in choosing "raw and cold food".

Please stay tuned to the CFS website ( for updates on Food Safety Day 2020.

Briefing of Activities

Food Safety Talks on Seasonal Food

Various kinds of seasonal foods are put on the market in different seasons.  If these speciality foods are not handled properly, it will incur food safety risks and easily lead to food poisoning. 

To enhance the trade's awareness of the food safety of seasonal foods, the CFS will, from time to time, arrange related talks or upload the relevant information to its website to suggest ways for the trade to assure food safety under a sound food management system.  Members of the trade or interested individuals are welcome to participate in these talks or visit the following website:

Upcoming Activities

Hong Kong Brands and Products Expo (2020)

The annual Hong Kong Brands and Products Expo is expected to be held at Victoria Park some time near the end of this year and the beginning of the next year.  As in previous years, CFS staff will set up a booth during the Expo to promote food safety and disseminate food safety messages to the public on site by distributing publicity leaflets, pamphlets and souvenirs.   CFS staff will also explore food safety issues with participants in a lively and interesting manner through on-stage interactive redemption games.   

You are welcome to visit the coming Expo to learn more about food safety.

Food Safety Q&A

What Are the "5 Keys to Food Safety"?

The CFS has been advocating to consumers the "5 Keys to Food Safety" put forward by the World Health Organization (WHO) as simple and effective ways to prevent foodborne illnesses.  They include: 

1.  Choose (Choose safe raw materials)
2.  Clean (Keep hands and utensils clean)
3.  Separate (Separate raw and cooked food)
 4.  Cook (Cook thoroughly)
5.  Safe Temperatures (Keep food at safe temperatures)

Truth Against Fallacy

Energy Bars – a Healthy Food Choice or a Hype?

Living in a fast-paced and hectic city, people favour prepackaged products for the sake of convenience.  Hence, many types of pocket-sized food bars, containing ingredients like grains, nuts, dried fruits, protein or plant protein, emerge on the market under various names such as "nutrition bar", "energy bar", "protein bar", "meal replacement bar", "breakfast cereal bar" and "diet bar".  Savvy marketing creates an impression that these food products are a healthy and nutritious choice as an alternative to a meal or for energy refill after exercise.  However, many of them leave a lot to be desired in terms of nutrition. 

Like any food, energy bars consist of macronutrients such as protein, carbohydrates and fat, as well as micronutrients like vitamins, minerals and essential fatty acids.  It is of note that many energy bars are high in carbohydrates ranging anywhere from 10 to 50 grams per bar, depending on the brand and the intended use.  They may contain complex carbohydrates (i.e. polysaccharides) like starch and dietary fibre in oats or rice, and simple carbohydrates (i.e. monosaccharides and disaccharides) such as sucrose, glucose and fructose.  Sugar and sweeteners such as polydextrose and sorbitol and food additives like maltodextrin are often added to energy bars during processing in order to improve the texture and sweetness levels to satisfy consumers' palates. 

While these products claim to help keep blood sugar at a moderate level for athletes, some energy bars produce a quick rush of blood sugar followed by a rapid drop, which is not much different from what occurs with the consumption of a candy bar or bread.

Digesting the Bar Facts: Read the Nutrition Label

Sugars are simple carbohydrates (monosaccharides and disaccharides) which provide energy (1 gram of sugars provides 4 kcal of energy).  Excess calories from foods high in free sugars can contribute to unhealthy weight gain and obesity, a higher risk of diabetes and other non-communicable diseases.  Free sugars mean all mono- and di-saccharides added to foods by manufacturers, cooks or consumers, plus sugars naturally present in honey, syrup and fruit juices.  The WHO sets out guidelines which recommend the public to reduce free sugars intake to less than 10% of the daily total energy intake for both adults and children, i.e. less than 50 grams of free sugars (about 10 sugar cubes) per day for an adult having a daily diet of 2,000 kcal. 

Consumers may be confused sorting through all the heavily-hyped promotional statements on the front package of energy bars.  To avoid exceeding the daily recommended intake level of free sugars, consumers are advised to read the ingredient list and compare the products.  Reading nutrition labels allows a better understanding of their sugar contents and calories, thus facilitating choosing these products to suit the individual's needs and activity level, and for weight-watching. 

After doing exercise, we need to replenish carbohydrates, protein and water in the body.  There are many fresh food alternatives that can readily meet these needs.  Portable fruits such as apples and bananas are healthier options.  They are convenient for consumption and can give a quick energy boost.  It is always better to have a simple yet healthy meal with adequate portions of fresh vegetables, fruits and grains.  When choosing snacks, consider healthy options such as fresh fruits and tomatoes, and bear in mind that calorie-dense energy bars are not the suitable snack choices.

Brain Gym

For Your Calculation

Which of the following energy bars is lower in sugars for consumption?

  1. Bar 1
    Serving size: 40g
    Sugar content: 54g/100g
  2. Bar 2
    Serving size: 45g
    Sugar content: 13.5g/100g

Bar 2

Sugar intake from consuming one Bar 1:
54g x 40/100
= 21.6g

Sugar intake from consuming one Bar 2
13.5g x 45/100
= 6.1g

Enquiries and Subscription

Printed copies of the Food Safety Express can be obtained from the Communication Resource Unit at Room 401, 4/F, Food and Environmental Hygiene Department Nam Cheong Offices and Vehicle Depot, 87 Yen Chow Street West, Sham Shui Po, Kowloon.  For enquiries, please call 2381 6096.