Biological Hazards in Food: Understanding Microbial Risks

According to the World Health Organization, unsafe food causes more than 600 million cases of foodborne illness and around 420,000 deaths every year. What’s alarming is that in most of these cases, the food looked, smelled, and tasted perfectly fine. The real threat was invisible – microscopic organisms that had already multiplied to dangerous levels. These are biological hazards, and understanding them is fundamental to safe food production, processing, and handling.

What are biological hazards in food? 🔗

Biological hazards are biological agents that have the capacity to cause harmful effects in humans. In the context of food safety, this means living microorganisms – including bacteria, viruses, parasites, and fungi – that can contaminate food at any stage of the supply chain, from farm to fork. Unlike chemical or physical hazards, biological hazards are alive and can multiply rapidly under the right conditions, making them particularly dangerous. Food can be contaminated both at the source as raw material, and during food processing up to storage and distribution. Infected food handlers and contaminated food contact surfaces can also spread microorganisms onto raw or processed food.

The main types of biological hazards 🔗

Bacteria 🔗

Bacteria are single-celled organisms and are generally considered the most important causative agents of foodborne illnesses. They thrive in warm, moist, protein-rich environments – which describes most of the food we eat. Bacteria cause illness in two distinct ways. Some, like Salmonella and Listeria monocytogenes, cause illness by infecting the body directly after being ingested. Others, like Staphylococcus aureus and Bacillus cereus, produce toxins inside the food itself, and it is these toxins – not the bacteria – that make people sick when they eat the contaminated food.

Salmonella is a major cause of bacterial foodborne illness globally, commonly associated with poultry, eggs, raw meat, and dairy products. Listeria monocytogenes is particularly dangerous because it can grow even under refrigeration, making it a serious concern for ready-to-eat foods. In reported foodborne outbreaks within the EU, bacterial agents – particularly Salmonella – accounted for the highest share of identified outbreak causes.

Viruses 🔗

Viruses are far smaller than bacteria and cannot reproduce outside a living host. However, they are incredibly resilient and can survive on surfaces and in food for extended periods. Norovirus is a common cause of foodborne infections and is characterized by nausea, vomiting, watery diarrhoea, and abdominal pain. Hepatitis A virus can also be transmitted by food and can cause long-lasting liver disease, typically spreading through raw or undercooked seafood or contaminated raw produce. Critically, the infective dose of most viruses is extremely small – sometimes as few as 10 viral particles – meaning only a tiny amount of contamination is needed to cause illness.

Parasites 🔗

Parasites are organisms that live in or on a host, deriving nutrients from it. In food, they are less common than bacteria or viruses but can cause severe and long-lasting health effects. Some parasites, such as fish-borne trematodes, are transmitted exclusively through food, while others like tapeworms (Echinococcus spp. and Taenia spp.) may infect people through food or direct contact with animals. Giardia lamblia and Cryptosporidium are commonly associated with contaminated water and raw vegetables. Trichinella can be present in undercooked pork and wild game. Human beings may get infected with parasitic worms through consumption of undercooked meat, freshwater fish, and snails.

Fungi and molds 🔗

Biological hazards also include fungi and molds, which are not visible to the naked eye and can contaminate food at any point in its distribution. While some molds are harmless, others produce mycotoxins – toxic compounds that can cause serious health problems even in small quantities. Molds typically grow on grains, nuts, fruits, and bread when storage conditions are humid or temperatures are poorly controlled.

Key indicators of microbial contamination 🔗

Because contaminated food often appears completely normal, food safety professionals rely on specific laboratory tests to detect and measure biological hazards. Three indicators are especially important in routine food quality monitoring.

Total Plate Count (TPC) 🔗

Total Plate Count (TPC), also known as the Aerobic Plate Count or Standard Plate Count, is one of the most fundamental microbiological tests in food safety. It estimates the number of viable bacteria in a food sample and is widely used as a general indicator of food hygiene, processing effectiveness, and shelf-life quality, following the internationally recognized standard ISO 4833-1:2013.

TPC works on a simple principle: a food sample is diluted, plated on nutrient agar, incubated, and the colonies that grow are counted. Results are expressed as colony-forming units per gram (CFU/g). A high TPC value may result from inadequate raw material quality, insufficient heat processing, post-processing contamination, poor hygiene practices, or improper storage. Elevated TPC often correlates with spoilage and reduced product shelf life.

It is important to understand what TPC does and does not tell you. TPC cannot differentiate between pathogenic and non-pathogenic bacteria. A high plate count indicates substantial bacterial presence but does not identify whether those bacteria pose direct health risks. It is best used as an overall hygiene indicator, triggering further targeted pathogen testing when counts are elevated.

E. coli as a contamination indicator 🔗

Escherichia coli (E. coli) is used in food safety as an indicator organism for fecal contamination. Most strains of E. coli are harmless and naturally present in the intestines of humans and animals, but their presence in food signals that fecal matter has entered the food supply – which means more dangerous pathogens could also be present from the same source.

However, certain strains are directly pathogenic. Shiga toxin-producing E. coli (STEC) has been associated with many foodborne outbreaks, linked to foods like unpasteurized juices, soft cheeses, and raw fruits and vegetables. Symptoms can include bloody diarrhoea and kidney failure, with deaths reported particularly among young children, the elderly, and immunocompromised individuals.

Common sources of E. coli contamination include undercooked ground beef, raw milk, contaminated irrigation water on fresh produce, and cross-contamination during food preparation. Monitoring E. coli levels is therefore a standard requirement in food safety programs worldwide, especially for products consumed raw or minimally processed.

Staphylococcus aureus 🔗

Staphylococcus aureus is a particularly challenging biological hazard because of the way it causes illness. S. aureus is a common commensal organism on human skin and mucous membranes, with estimates of 20-30% for persistent colonization and up to 60% for intermittent colonization in the general population. This makes food handlers the primary source of contamination in food production environments.

The real danger lies in the toxins. Staphylococcal food-borne disease (SFD) results from the contamination of food by preformed S. aureus enterotoxins, which are heat-stable and among the most common causes of reported foodborne diseases worldwide. This means that even thorough cooking will not destroy these toxins once they have already formed in the food. S. aureus can grow across a wide temperature range of 7-48.5°C, and toxin production begins from 10°C, making temperature control critical to preventing its proliferation.

Foods commonly associated with S. aureus contamination include cream-filled pastries, sliced meats, salads, sandwiches, and other protein-rich foods with significant hand contact. Symptoms of staphylococcal food-borne disease include nausea, vomiting, and abdominal cramps with or without diarrhoea, typically appearing within 30 minutes to 6 hours after consuming contaminated food.

How biological hazards enter the food chain 🔗

Several biological hazards are soilborne and are considered environmental contaminants, originating from the soil and transferring to crops, vegetables, and fruits. Some airborne pathogens can travel through spores and grow on foods once they land on them. Pests like rodents and insects can also act as carriers, spreading harmful bacteria and viruses through contact with food. Cross-contamination during food preparation – such as using the same cutting board for raw meat and ready-to-eat vegetables – is another common pathway. Poor personal hygiene among food handlers, inadequate storage temperatures, and use of contaminated water are all well-established routes of microbial entry into the food chain.

Preventing biological hazards: core practices 🔗

Prevention is the most effective strategy in food safety. To prevent illness from bacteria and viruses, food safety steps should always include: clean, separate, cook, and chill. These four principles address the main mechanisms through which biological hazards cause harm.

Personal hygiene and sanitation 🔗

Because food handlers are a primary source of pathogens like S. aureus and Norovirus, personal hygiene is non-negotiable. Thorough handwashing with soap and water before handling food, after using the restroom, and after contact with raw ingredients is essential. People with open wounds, skin infections, or respiratory illness should not have direct contact with food, food ingredients, or food utensils. Regular cleaning and disinfection of food contact surfaces, equipment, and processing environments is equally critical to preventing biofilm formation, where bacterial communities can persist and resist standard sanitizing efforts.

Cooking and temperature control 🔗

Cooking food to the correct internal temperatures kills most pathogenic bacteria and inactivates many viruses. However, as seen with S. aureus, cooking cannot reverse contamination once heat-stable toxins have already formed. This makes temperature control during storage just as important as the cooking step itself. Keeping cold foods below 5°C and hot foods above 60°C prevents bacteria from multiplying to dangerous levels. Keeping foods at refrigerated temperatures prevents bacteria from growing to hazardous levels.

Proper storage and cross-contamination prevention 🔗

Raw meats, poultry, and seafood must always be stored separately from ready-to-eat foods to prevent cross-contamination. Proper packaging and sealed containers reduce exposure to environmental contaminants. First-in, first-out (FIFO) stock rotation minimizes the risk of spoilage and the growth of spoilage organisms that signal compromised hygiene.

Regular monitoring and testing 🔗

Systematic monitoring is the backbone of any food safety management system. Food producers can develop prevention measures by determining the sources and causative pathogens of foodborne illnesses, and can adopt comprehensive testing as part of their food safety plan to identify risks and develop robust processes to protect consumers. Monitoring programs should combine TPC testing with targeted pathogen tests for organisms like Salmonella, E. coli, and S. aureus, as well as environmental sampling of processing surfaces, drains, and water sources. The WHO works with member states through scientific risk assessments and risk management guidelines to strengthen national capacity to prevent and control foodborne diseases.

The global burden and why it matters 🔗

Diarrhoeal diseases – the most common illnesses resulting from contaminated food – cause approximately 550 million people to fall ill and 230,000 deaths every year globally. Children under five years of age are disproportionately affected, carrying 40% of the total foodborne disease burden. Beyond the human cost, foodborne illnesses impose enormous economic losses through healthcare costs, reduced productivity, damage to food industry reputations, and trade disruptions. An estimated US$110 billion is lost each year in productivity and medical expenses from unsafe food in low- and middle-income countries alone. Addressing biological hazards in food is therefore not just a technical concern – it is a public health, economic, and social priority.

What do you think? Given that biological hazards like S. aureus toxins can survive cooking temperatures, do you believe current food handling training adequately prepares workers for these less visible risks? And considering that TPC only gives a general picture of microbial load without identifying specific pathogens, how should food businesses balance routine TPC monitoring with more targeted pathogen testing in their quality assurance programs?

References

1. https://www.who.int/news-room/fact-sheets/detail/food-safety
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