Foodborne Illness and Contamination
Most illness questions reward knowing an organism's route and timing rather than its name. Start by sorting hazards into biological, chemical, and physical.
Biological hazards
Bacteria need FATTOM - food, acidity, temperature, time, oxygen, moisture. The temperature danger zone is 41°F to 135°F, with the fastest growth roughly between 70°F and 125°F. Spore-formers survive normal cooking: Clostridium perfringens (meat, gravy, slow cooling), Bacillus cereus (rice and starchy foods), and Clostridium botulinum (low-acid canned or anaerobic packaging). Staphylococcus aureus lives on skin and hands and produces a heat-stable toxin, so reheating does not make the food safe. Listeria grows at refrigeration temperatures. Salmonella and Campylobacter arrive with poultry and cross-contamination; E. coli O157:H7 with undercooked ground beef and contaminated produce.
Viruses do not multiply in food. Norovirus and Hepatitis A spread through infected hands, ready-to-eat food, and shellfish from contaminated water. Parasites such as Anisakis in fish, Trichinella in pork, and Cyclospora are controlled by proper cooking and, where required, freezing.
Chemical hazards include sanitizer residue, unapproved additives, and allergens; physical hazards include glass, metal, and bones.
Traps
Symptoms starting 1–6 hours after a banquet featuring rice or gravy point to toxin formation, not infection. A food handler with diarrhea points to Norovirus or Shigella. Cooking does not fix allergen cross-contact. The Big Six - Norovirus, Hepatitis A, Salmonella Typhi, Shigella, E. coli O157:H7, and nontyphoidal Salmonella - trigger exclusion and reporting to the regulatory authority.