Viruses in food

Viruses in Food : The Things You Don’t Want To Know About Stomach Flu

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There are 2 main viruses in food that are involved with food poisoning. But before we get there, lets go through the basics.

What are viruses?

A virus is micro-organism that is designed to infect its host. The primary purpose on this micro-organism  Is to ‘deliver’ its DNA / RNA into a host cell. Viruses are parasites (meaning they need another organism to survive) and are generally smaller than bacteria.

You can see bacteria under a normal microscope, and need an election microscope to be able to see viruses. Viruses are measured in nanometers (nm) and bacteria is micrometers (ūm). There are 1000 ūm in 1 millimetre (mm) and 1 million nm in 1 mm.

There are millions are different types of viruses and unlike bacteria, none are good for you. Viruses come in variety of shapes:

The most common viruses we hear about daily are  HIV , Influenza & Ebola. As mentioned, the primary focus of a virus to replicate its DNA / RNA and can infect a variety of hosts in a few ways.

Here we’ll focus on Food Viruses.

Viruses in Food

There are 2 main viruses in food that are involved with food poisoning. Hepatitis A & Noroviruses. Although bacteria are the most common food poisoning organisms, viruses in food do play a role in food safety.

 The foods that seem to be most responsible for viral infection are those with little to no processing. These include foods such as oysters, clams, mussels and scollops as well as fresh produce (salads and fruits).

Hepatitis A

The hepatitis A virus is one of several types of hepatitis viruses that affect your liver’s ability to function. Hep A infections occur from consuming contaminated food or water, exactly the same way as bacteria.  The main difference is, that the virus is contagious and you can get infected by having close contact with another person that is infected.

Remember, viruses primary function is to replicate!

Mild cases of infection don’t requirement treatment and usually your body can resolve the infection itself. Severe cases do result in permanent liver damage.


Hep A infection symptoms take a few weeks to show, while the virus in multiplying in our body. By the time you show symptoms, you’ve likely infected other people.

Symptoms include:

  • Sudden nausea and vomiting
  • Fatigue
  • Low-level fever
  • Joint pain
  • Abdominal pain or discomfort, especially on the upper right side beneath your lower ribs (by your liver)
  • Loss of appetite

Really not that different from any food poisoning experience.

Who are at risk?

  • Those with compromised immune-systems.
  • Those who visit / live / work in regions where Hep A is common
  • Those
  • People with chronic liver disease
  • Small children & Pregnant moms

Where do the infections come from?

Hep A’s primary mode of infection is via the faecal-oral route rather than through sneezing and coughing. This means infection occurs from consuming:

  • Contaminated or untreated water
  • Raw shellfish
  • Consuming foods that were handling by an infected person
  • Coming into close contact with an infected individual


Noroviruses are the most common cause of acute gastroenteritis. This is more commonly know as the stomach flu or viral gastroenteritis. Noroviruses are also spread by consuming food and water that is contaminated. Noroviruses are highly contagious and anyone can get infected like flu. 

Norovirus infection in mild cases are usually the 24hr bug and can take 1 or 3 days to recover. Severe cases result in dehydration and need hospitalisation.

Infections occurs most frequently in closed and crowded environments such as hospitals, nursing homes, child care centres, schools and cruise ships. In fact most resorts cases of food poisoning on cruise ships are as a result of Norovirus infection!


  • Nausea
  • Vomiting
  • Abdominal pain or cramps
  • Muscle pain

Who are at risk?

As mentioned Noroviruses are very contagious and anyone can get the stomach bug. However, those that are more severely affected include the high risk population:

  • Babies & small children
  • Pregnant moms
  • Elderly
  • Those that are immune-compromised

Where do the infections come from?

  • Contaminated or untreated water
  • Ready-to-eat foods touched by infected food workers (salads, sandwiches, ice, cookies, fruit)
  • Raw shellfish
  • Consuming foods that were handling by an infected person
  • Coming into close contact with an infected individual

Several of the documented outbreaks of viral food-borne illness have been linked to contamination of the food by an infected food handler, rather than the contaminated raw product.

In the case of shellfish and specifically oysters and the like, are that their environments are increasingly exposed to human faecal matter through raw sewerage waste. These oysters are “filter feeders” and collect viruses and “store them in their “guts”. Ready and waiting for us to consume them.

Severe Hep A infections are one of more dangerous in terms of outbreaks, because they can have life long effects on the liver.

Food Safety & Viruses

Virus detection in a food safety system is a complicated matter, and only in recent years has it been given any attention. This is mostly because of the costs involved in the tests need to detect viruses as compared to simple detection of bacteria.

Viral food poisoning tends to happen quicker and is shorter lived than bacterial food poisoning. And require expensive equipment for find viruses in food.

Fortunately, we know that these viruses and bacteria have the same infection routes, Fecal-oral. So although there never any guarantee that both bacteria and viruses are present in a food, these use of E.coli as an indicator organism, especially of fecal contamination can help in the prevention of viral infections via food.

What is means, is that if E.coli is present in a food, especially oysters etc, there is a good chance that Hep A or Noroviruses are present as well.

Preventing Viruses in Foods

The first and very clear way to prevent viruses in food is to stop contamination at the source. For oysters, this means oyster farming  where the environment is controlled and prevent sewerage from entering the system. The same principle can be applied to vegetable and fruit farming where the water quality is managed.

One of the biggest suspects of food contamination in farming is related to sewerage entering the water supply used to irrigate crops. In the case of bacteria  it is also organic farming using untreated cattle manure that presents risks.

Secondly, maintain good personal hygiene, and managing staff that are sick is a critical aspect of prevention. This is especially true in the cheffing industry where you work until you drop, and even then you better be in hospital. 

Lastly, managing a good food safety system, where the focus is on bacteria, will ultimately help in risk prevention.

We feel that the only additional requirement for managing viruses in food is by know where your foods are sourced from. And having strict requirements when it comes to oysters, mussels, clams and scollops.

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