Foodborne Illness, Contamination and Prevention
What this domain tests
Questions test your ability to recognise causes of foodborne illness, distinguish infection from intoxication, identify biological, chemical and physical contamination, and choose controls that match the hazard.
Core rules
- Infection results from eating live pathogens that grow in the gut, for example Salmonella, Campylobacter, E. coli O157 and norovirus.
- Intoxication results from toxins already formed in food, for example Staphylococcus aureus toxin and Bacillus cereus toxin.
- High-risk foods are moist, protein-rich and ready-to-eat: cooked rice, meat, dairy, eggs, seafood, gravies and cut fruit.
- Prevent growth with rapid cooling, refrigeration at or below 5°C, hot holding above 63°C and limiting time in the danger zone.
- Destroy pathogens by thorough cooking and safe reheating.
- Prevent recontamination through handwashing, clean utensils and separation of raw and cooked food.
- Chemical hazards include pesticides, cleaning chemicals and aflatoxin in mouldy maize and groundnuts. Aflatoxin is heat-stable, so cooking does not remove it.
Worked example
Cooked rice is left on a warm counter overnight and fried the next morning. Bacillus cereus spores survive cooking, germinate at room temperature and produce a heat-stable toxin. Reheating kills bacteria but not the toxin, so illness can still occur. Correct practice: cool rice rapidly, refrigerate within two hours, keep refrigerated, and reheat once to 75°C.
Traps that cost marks
- The last meal eaten is not always the source; incubation periods vary.
- Mayonnaise is not automatically the cause; raw eggs, rice, meat and water are common vehicles.
- Reheating does not destroy pre-formed toxins.
- Mouldy maize cannot be made safe by cooking or trimming.
- A single case can be a foodborne illness; outbreaks need investigation, not assumption.