Foodborne Illnesses: Types, Causes, and Prevention

Every year, nearly 600 million people worldwide fall sick after eating contaminated food, and about 420,000 of those cases end in death. These are not just statistics – they represent a massive, largely preventable public health challenge. Foodborne illnesses occur when people consume food or beverages contaminated with harmful microorganisms, their toxins, or chemical substances. Understanding how these illnesses work, what causes them, and how to prevent them is essential for anyone handling, preparing, or consuming food – especially meat and animal-origin products.

What exactly is a foodborne illness? 🔗

A foodborne illness is any disease that results from eating or drinking contaminated food or beverages. The contamination can come from bacteria, viruses, parasites, toxins, or chemical substances. These agents enter the body through the gastrointestinal tract, which is why the most common symptoms tend to be gastrointestinal – nausea, vomiting, diarrhoea, abdominal cramps, and fever.

Symptoms can appear within minutes or take days or even weeks to show up, depending on the specific pathogen involved. Because many of these symptoms overlap with common stomach flu, a large number of foodborne illnesses go undiagnosed and unreported. In the United States alone, the CDC estimates that roughly 48 million people get sick, 128,000 are hospitalised, and 3,000 die from foodborne diseases annually.

Three categories of foodborne illness 🔗

Foodborne illnesses are broadly classified into three categories based on how the disease-causing agent affects the body: foodborne infections, foodborne intoxications, and toxin-mediated infections (also called toxico-infections). Each category has a distinct mechanism, and understanding this distinction is key to both diagnosis and prevention.

Foodborne infections 🔗

A foodborne infection occurs when a person consumes food containing live pathogenic microorganisms – bacteria, viruses, or parasites – that then invade and multiply inside the body. The pathogens typically colonise the intestinal lining, and some may even spread to other parts of the body through the bloodstream.

Because the microorganisms need time to multiply after ingestion, foodborne infections generally have a longer incubation period, often measured in days rather than hours. Common symptoms include fever, diarrhoea, abdominal pain, and nausea.

Some well-known examples of foodborne infections include:

Salmonellosis – Caused by Salmonella bacteria, this is one of the most common foodborne infections globally. It is typically linked to raw or undercooked eggs, poultry, and unpasteurised milk. Symptoms usually last four to seven days and include fever, cramps, and diarrhoea.

Campylobacteriosis – Caused by Campylobacter jejuni, this infection is commonly traced to raw or undercooked poultry, unpasteurised milk, and contaminated water. In rare cases, it can lead to Guillain-Barré syndrome, a serious neurological condition.

Listeriosis – Caused by Listeria monocytogenes, this infection is particularly dangerous for pregnant women, newborns, the elderly, and immunocompromised individuals. Listeria can grow even at refrigeration temperatures, making it an especially insidious threat in ready-to-eat foods and unpasteurised dairy products.

Norovirus infection – Norovirus is the most common viral cause of foodborne illness, responsible for millions of cases each year. It spreads easily through contaminated food, water, and person-to-person contact, and causes sudden-onset vomiting, diarrhoea, and stomach cramps.

Foodborne intoxications 🔗

Unlike infections, foodborne intoxications do not require live organisms to enter the body. Instead, they occur when a person eats food that already contains preformed toxins – toxic substances produced by bacteria or other sources while the food was improperly stored or handled. The organisms themselves may or may not still be present in the food at the time of consumption; it is the toxin that causes the illness.

Because the harmful toxin is already present in the food, intoxications tend to have a much shorter onset time – often just minutes to a few hours. The body reacts quickly, usually through vomiting or diarrhoea, as it tries to expel the toxic substance.

Key examples of foodborne intoxications include:

Staphylococcal food poisoning – Staphylococcus aureus bacteria, commonly found on human skin and in the nose, can contaminate food through improper handling. The bacteria multiply rapidly at room temperature and produce heat-stable toxins. Symptoms like severe nausea, vomiting, and cramps can appear within one to six hours of eating contaminated food.

Botulism – Caused by the toxin of Clostridium botulinum, this is one of the most severe forms of food intoxication. The toxin attacks the nervous system, and symptoms typically appear within 18 to 36 hours, though they can show up in as few as four hours. Improperly canned or vacuum-packed foods are the most common sources. Without prompt medical treatment, botulism can be fatal.

Bacillus cereus poisoning – This bacterium, commonly found in soil, can contaminate starchy foods like rice, pasta, and potatoes. It produces toxins that cause either a vomiting-type illness (onset within 0.5 to 6 hours) or a diarrhoeal-type illness (onset within 8 to 16 hours).

Toxin-mediated infections (toxico-infections) 🔗

This third category sits between infection and intoxication. In a toxin-mediated infection, a person ingests living microorganisms along with the food. These organisms then colonise the intestinal tract and produce toxins inside the body. The critical distinction from intoxication is that the toxin is not preformed in the food – it is produced within the host after the organism has been consumed and has begun to grow.

The classic example of a toxin-mediated infection is:

Clostridium perfringens – Often called “the cafeteria germ,” C. perfringens is commonly associated with foods that are prepared in large quantities and kept warm for extended periods, such as at buffets or catered events. The bacteria are destroyed by proper cooking, but their spores can survive and germinate if food is held in the temperature danger zone (between 40°F/4°C and 140°F/60°C). Once consumed, the bacteria produce a toxin in the intestines that causes diarrhoea and abdominal cramps, typically within 8 to 12 hours.

Common causative agents of foodborne illness 🔗

A wide range of biological and chemical agents can cause foodborne illness. Here is a closer look at the major categories.

Bacteria 🔗

Bacteria are the most commonly identified cause of serious foodborne illness. According to the World Health Organization, Salmonella, Campylobacter, and enterohaemorrhagic Escherichia coli are among the most prevalent bacterial pathogens, affecting millions of people every year. Other significant bacteria include Listeria monocytogenes, Vibrio species (found in raw or undercooked seafood), and Shigella species.

Viruses 🔗

Norovirus and Hepatitis A are the two most significant foodborne viruses. Norovirus causes sudden vomiting and diarrhoea and spreads very easily. Hepatitis A can cause long-lasting liver disease and is most commonly associated with raw or undercooked shellfish and contaminated produce.

Parasites 🔗

Parasites like Giardia, Cryptosporidium, Toxoplasma gondii, and various tapeworm species (Taenia) can enter the food chain through contaminated water, soil, or undercooked meat. Parasites cannot multiply in food but survive in it until consumed, at which point they colonise the host.

Chemicals and natural toxins 🔗

Not all foodborne illnesses are caused by living organisms. Naturally occurring mycotoxins (produced by moulds on grains), marine biotoxins (in shellfish), heavy metals like lead and mercury, and environmental pollutants like dioxins and PCBs can also contaminate food and cause acute or chronic health problems.

Who is most at risk? 🔗

While anyone can contract a foodborne illness, certain groups face significantly higher risk of severe illness or complications. These high-risk groups include:

Infants and young children – Their immune systems are still developing, making them more vulnerable. Children under five carry a disproportionately large share of the global foodborne disease burden.

Pregnant women – Pregnancy-related immune changes increase susceptibility to pathogens like Listeria, which can cause miscarriage, stillbirth, or severe illness in newborns.

Older adults – Aging weakens the immune system and reduces the body’s ability to fight off infections effectively.

Immunocompromised individuals – People with conditions such as HIV/AIDS, cancer, diabetes, or organ transplant recipients have weakened defences against pathogens.

How does food become contaminated? 🔗

Food can become contaminated at any point in the supply chain – during production, processing, transportation, storage, or preparation. Some of the most common contamination pathways include:

Cross-contamination – This happens when harmful microorganisms are transferred from one food item (usually raw meat or poultry) to another through shared utensils, cutting boards, or hands. It is one of the most common and preventable causes of foodborne illness in home kitchens.

Inadequate cooking – Many pathogens in raw meat, poultry, seafood, and eggs are killed at specific temperatures. Undercooking allows these organisms to survive and cause illness.

Improper storage – Leaving perishable food at room temperature allows bacteria to multiply rapidly in what food safety experts call the “danger zone” – temperatures between 4°C and 60°C (40°F to 140°F).

Poor personal hygiene – Food handlers who do not wash their hands properly after using the toilet, handling raw food, or touching contaminated surfaces can easily transfer pathogens to food.

Contaminated water or soil – Using unsafe water for irrigation, washing, or food preparation can introduce pathogens or chemical contaminants into the food supply.

Prevention: the four pillars of food safety 🔗

The good news is that most foodborne illnesses are preventable. The U.S. Centers for Disease Control and Prevention (CDC) recommends following four core steps: Clean, Separate, Cook, and Chill. These align closely with the WHO’s Five Keys to Safer Food.

Clean: wash hands and surfaces often 🔗

Handwashing is the single most effective way to prevent the spread of foodborne pathogens. Wash your hands with soap and warm water for at least 20 seconds before, during, and after preparing food, and especially after handling raw meat, poultry, eggs, or seafood. Utensils, cutting boards, and countertops should be washed with hot, soapy water after each use. Fresh fruits and vegetables should be rinsed under clean running water before consumption.

Separate: prevent cross-contamination 🔗

Keep raw meat, poultry, seafood, and eggs separate from ready-to-eat foods – during shopping, storage, and preparation. Use separate cutting boards for raw animal products and fresh produce. Never place cooked food on a plate that previously held raw meat without washing it first.

Cook: reach safe internal temperatures 🔗

Cooking food to the correct internal temperature is the most reliable way to kill harmful microorganisms. Use a food thermometer – visual cues like colour and texture are not reliable indicators of doneness. Key temperatures include 74°C (165°F) for poultry and leftovers, 71°C (160°F) for ground meats, and 63°C (145°F) for whole cuts of beef, pork, and fish.

Chill: refrigerate promptly 🔗

Perishable food should be refrigerated within two hours of preparation (or within one hour if the ambient temperature exceeds 32°C/90°F). Keep refrigerators at or below 4°C (40°F) and freezers at or below -18°C (0°F). Thaw frozen foods in the refrigerator, in cold water, or in the microwave – never on the countertop at room temperature.

Additional preventive measures 🔗

Beyond the four core steps, several other practices play an important role in reducing foodborne illness risk:

Choose safe and fresh raw materials – Buy pasteurised milk and dairy products. Avoid consuming raw or undercooked eggs, and be cautious with raw seafood. Check expiry dates and inspect packaging for damage before purchasing.

Use safe water – Whether for drinking, cooking, or cleaning food, always ensure the water is safe. If there is any doubt, boiling water before use is a simple and effective precaution.

Store food correctly – Keep hot foods hot (above 60°C) and cold foods cold (below 4°C). Do not overload refrigerators, as this prevents food from cooling quickly enough at the core. Use sealed containers to prevent contamination during storage.

Reheat thoroughly – When reheating leftovers, make sure all parts of the food reach at least 74°C (165°F). This kills any bacteria that may have multiplied during storage.

Be aware of food recalls – Stay informed about food recall notices from regulatory authorities. If you have a recalled product at home, discard it immediately and clean the storage area.

The global and economic impact 🔗

Foodborne illnesses are not just a health issue – they carry enormous economic consequences. The WHO reports that low- and middle-income countries lose approximately US$110 billion every year in productivity and medical costs due to unsafe food. These diseases strain healthcare systems, reduce workforce productivity, and can severely damage a country’s food trade and tourism sectors.

Children under five bear a disproportionate share of the burden, with an estimated 125,000 deaths every year. In many parts of the world, a lack of access to clean water, proper sanitation, and adequate refrigeration exacerbates the problem, making food safety an issue of equity as much as public health.

The role of food producers and regulators 🔗

While individual hygiene and kitchen practices are critical, food safety is ultimately a shared responsibility across the entire food chain. Farmers, food processors, distributors, retailers, and regulators all play a role. Systems like Hazard Analysis and Critical Control Points (HACCP) are used in food production and processing to identify and control potential hazards at every stage. Government agencies like the USDA’s Food Safety and Inspection Service (FSIS), the FDA, the CDC, and international bodies like the WHO and FAO’s Codex Alimentarius Commission set standards and guidelines to protect public health.

What do you think? Given that most foodborne illnesses are preventable, why do you think they remain so widespread – is it a gap in awareness, infrastructure, or personal habits? And in your experience, which food safety practice do you find most difficult to consistently follow?

References

1. https://www.who.int/news-room/fact-sheets/detail/food-safety
2. https://www.cdc.gov/food-safety/about/index.html
3. https://hhs.iowa.gov/epi-manual-guide-surveillance-investigation-and-reporting/foodborne-outbreak-investigation/appendix
4. https://www.hawaiipacifichealth.org/healthier-hawaii/safety-corner/6-common-foodborne-illnesses-how-to-prevent-them/
5. https://pmc.ncbi.nlm.nih.gov/articles/PMC6604998/
6. https://www.env.nm.gov/wp-content/uploads/sites/9/2019/10/foodborne_illness_ref.pdf
7. https://dchealth.dc.gov/service/foodborne-infections-and-intoxications
8. https://www.fsis.usda.gov/food-safety/foodborne-illness-and-disease
9. https://www.health.state.mn.us/people/foodsafety/prevention.html
10. https://www.cdc.gov/food-safety/prevention/index.html
11. https://www.paho.org/en/health-emergencies/who-golden-rules-safe-food-preparation
12. https://www.osha.gov/foodborne-disease