Foodborne Illnesses and Food Hazards (Biological, Chemical, Physical)
Three hazard families
Biological - bacteria, viruses, parasites, and their toxins. Common exam names: Salmonella (poultry, eggs), Campylobacter (raw poultry), E. coli O157 (undercooked beef, contaminated water), Staphylococcus aureus (hands, skin lesions, toxin is heat-stable), Bacillus cereus (cooked rice left warm), Clostridium perfringens (stews, gravies cooled slowly), Listeria (chilled ready-to-eat foods), norovirus and hepatitis A (handlers, water, shellfish).
Chemical - cleaning and sanitising agents, pesticides, lubricants, veterinary residues, mycotoxins such as aflatoxin in mouldy peanuts, and undeclared allergens.
Physical - glass, metal fragments, hard plastic, stones, bone, hair, pests, and packaging pieces.
Why some hazards are riskier
Bacteria need food, moisture, time, warmth, and often oxygen-free conditions. High-risk foods are moist, protein-rich, and near-neutral: meat, poultry, seafood, eggs, dairy, cooked rice, and gravy. Spore-formers survive normal cooking, so cooling and holding control them.
Worked example
A caterer cooks a large pot of rice at 10 a.m., leaves it on the counter, and fries it at 4 p.m. The rice sits in the danger zone for six hours. Bacillus cereus spores survive cooking, germinate, and produce toxin; reheating does not destroy the toxin. Correct controls: cool rapidly in shallow trays, refrigerate, and hold hot food at 60 °C or above.
Traps that cost marks
- Assuming reheating destroys all toxins - staphylococcal and B. cereus toxins are heat-stable.
- Calling mould on peanuts a "physical" hazard - it is chemical (mycotoxin).
- Forgetting allergens, which are chemical hazards requiring labelling and separation.
- Naming a pathogen without linking it to a food vehicle or control.