Foodborne Illness and Risk Factors
This domain tests the biology behind the rules: which organisms cause illness, which foods carry them, and why certain controls work.
Growth requirements
Bacteria need food, pH above 4.6, temperatures in the 41–135°F danger zone, time, moisture (water activity above 0.85), and appropriate oxygen. TCS foods support rapid growth: meat, poultry, seafood, dairy, shell eggs, cut melons and tomatoes, leafy greens, cooked rice and beans, sprouts, and untreated garlic-and-oil mixtures.
Organisms to know
- Norovirus: ready-to-eat food touched by an infected handler; very low infectious dose; survives freezing; hand sanitizer is not a substitute for washing.
- Hepatitis A: fecal-oral, infected handler, RTE foods; jaundice is the warning sign.
- Salmonella Typhi and nontyphoidal Salmonella: poultry, eggs, produce.
- Shigella: RTE foods, water, poor handwashing.
- E. coli O157:H7 (STEC): raw ground beef, leafy greens, unpasteurized juice; bloody diarrhea.
- Listeria monocytogenes: deli meats, soft cheese, smoked seafood; grows at refrigeration temperature and is most dangerous to pregnant, elderly, and immunocompromised people.
- Staphylococcus aureus and Bacillus cereus (emetic type): toxins are heat-stable, so reheating does not make the food safe.
- Clostridium botulinum: anaerobic, low-acid, canned or vacuum-packed foods.
- Parasites: Anisakis in raw fish (freezing kills it), Trichinella in pork (cooking kills it).
Worked example
A customer becomes ill after eating sliced deli turkey. The slicer is wiped once daily with no sanitizer step. Listeria is the concern: it grows at 41°F, persists on slicer surfaces, and the product is RTE with no cooking kill step. The fix is full disassembly, cleaning, and sanitizing every 4 hours of use, not a temperature change.
Traps
Assuming freezing kills all pathogens; believing reheating destroys staph toxin; forgetting viruses do not multiply in food but stay infectious.