Viruses in Food: The Hidden Threat to Food Safety

There are two main viruses in food that are involved with food poisoning outbreaks. However, before examining these specific pathogens, it is vital to understand the biological basics. A virus is a micro-organism designed specifically to infect its host. Its primary purpose is to deliver its DNA or RNA into a host cell. Unlike bacteria, viruses are obligate parasites; they cannot survive or replicate without a living host.

The scale of these organisms is immense. While bacteria can be observed under a standard optical microscope, viruses require an electron microscope for visualisation. Viruses are measured in nanometres (nm), whereas bacteria are measured in micrometres (µm). To put this in perspective, there are 1,000 µm in a single millimetre, and one million nm in that same millimetre.

There are millions of different types of viruses, and unlike bacteria—where many strains are beneficial for gut health or food production—none are considered good for human health. They appear in a variety of shapes, from icosahedral to helical. While we frequently hear about Influenza or HIV, our focus within the HFS framework remains on foodborne viral infections.

2.0 Primary Viruses in Food

The two primary viruses responsible for foodborne illness are Hepatitis A and Noroviruses. While bacteria are statistically more common in food poisoning cases, viruses play a critical role because they are highly contagious and often harder to detect in routine kitchen environments.

Hepatitis A: The Liver Pathogen

The Hepatitis A virus affects the liver’s ability to function properly. Infections typically occur through the consumption of contaminated food or water. However, a major differentiator between viral and bacterial infection is that Hepatitis A is highly contagious through person-to-person contact. Severe cases can lead to permanent liver damage, though mild cases often resolve without specific treatment.

Symptoms of Hepatitis A can take several weeks to manifest as the virus multiplies within the body. This creates a dangerous window where an infected food handler may spread the virus to others before they even realise they are sick. Symptoms include:

• Sudden nausea and vomiting.
• Profound fatigue and low-level fever.
• Joint pain and abdominal discomfort, particularly on the upper right side near the liver.
• Loss of appetite and jaundice.

Those at highest risk include individuals with compromised immune systems, small children, pregnant mothers, and those with pre-existing chronic liver disease.

3.0 Noroviruses: The Cruise Ship Virus

Noroviruses are the most common cause of acute gastroenteritis, often referred to as the “24-hour bug” or stomach flu. They are notoriously contagious, thriving in closed, crowded environments like hospitals, nursing homes, and cruise ships. In fact, the majority of mass food poisoning events on luxury liners are attributed to Norovirus rather than bacterial contamination.

Symptoms usually include intense nausea, vomiting, abdominal cramps, and muscle pain. While most healthy adults recover in one to three days, the primary danger is dehydration, which frequently requires hospitalisation for the elderly or the very young.

4.0 Contamination Sources: Shellfish and Produce

The foods most responsible for viral outbreaks are those with minimal processing. Oysters, clams, mussels, and scallops are “filter feeders.” If they are grown in water contaminated with raw sewage, they collect and concentrate viruses within their digestive tracts. When consumed raw or undercooked, these viruses are delivered directly to the consumer.

Fresh produce, such as salads and fruits, are the second most common vector. These items can be contaminated at the farm through untreated irrigation water or in the kitchen by an infected food worker. Evidence shows that most documented outbreaks are linked to the hands of the food handler rather than the product itself.

5.0 Prevention and the Indicator Principle

Detecting viruses in a food safety system is complex and expensive, often requiring specialised equipment that far exceeds the cost of standard bacterial testing. However, the HFS Blueprint utilizes the “Indicator Principle.” Because viruses and bacteria like E. coli share the same infection routes—primarily faecal contamination—we use E. coli as a proxy.

If E. coli is detected in a batch of oysters or a water supply, it confirms faecal contamination. By default, there is a high probability that Hepatitis A or Noroviruses are also present. Therefore, an E. coli failure must be treated as a potential viral threat.

6.0 Strategic Prevention Steps

Prevention requires a multi-layered approach starting at the source of the product:

1. Source Management: Only purchase shellfish from reputable oyster farming operations where water quality is strictly monitored to prevent sewage ingress.
2. Personal Hygiene: Maintain impeccable personal hygiene. In the cheffing industry, there is a culture of “working until you drop,” but a Chef with Norovirus can shut down an entire restaurant. Sick staff must be excluded from the kitchen immediately.
3. Receiving Controls: Know exactly where your foods are sourced. Require shellfish tags and traceability for every delivery.

Ultimately, managing a food safety system focused on bacteria will provide a strong foundation for viral prevention. By managing the same risks—faecal contamination, hand hygiene, and water quality—you effectively neutralise the threat of both Hepatitis A and Norovirus.

Want to ensure your staff are properly trained in viral prevention? Read our guide on Critical Hand Washing Procedures or explore the Pathogenic Bacteria list for more information on indicator organisms.