Wedding Lunch Food Poisoning: Curd Rice or Chicken?
A marriage hall in Trichy catered lunch for 450 guests. Cooking began at 06:00. Chicken pulao was cooked at 08:30 and held in insulated boxes at 55–58°C until service at 12:30. Curd rice was prepared at 07:00, kept in steel vessels in the service hall at 31°C, and served from 12:30 to 14:00. Paneer gravy was reheated once at 11:30. By 21:00, 62 guests reported vomiting and diarrhoea; 11 were hospitalised. The cook had a bandaged cut on his index finger and worked without gloves. The hand-wash basin had no soap; the water source was a borewell. Leftover curd rice had a pH of 5.1. Stool samples were sent to the lab, but reports are awaited. The hall manager wants to blame the chicken.
1. Rank the three suspect foods by risk, using time-temperature data and the symptoms, and explain why the chicken may not be the main vehicle.
Read the worked answer
Ranking by time-temperature risk:
- Curd rice: cooked at 07:00, held 5.5–7 hours at 31°C, pH 5.1, served over 1.5 hours. This is a low-acid, moist, warm food with ideal conditions for Bacillus cereus and other spore-formers.
- Paneer gravy: reheated once at 11:30. If it cooled slowly afterwards, it is a risk, but a single reheat is less risky than 6 hours at 31°C.
- Chicken pulao: held at 55–58°C, below the 60°C hot-holding threshold, so it is a risk, especially for Clostridium perfringens. But the insulated hold and shorter time make it less likely than the curd rice.
The manager's blame on chicken ignores the curd rice's much worse profile. Symptoms began by 21:00, within 8–10 hours of lunch. Vomiting and diarrhoea fit both B. cereus and S. aureus, and the cook's infected finger makes S. aureus plausible. Lab results are needed before blaming one food.
2. Name two organisms that fit the evidence and state what laboratory or interview evidence would distinguish them.
Read the worked answer
Two organisms fit:
- Bacillus cereus: rice and curd rice held warm; emetic type causes vomiting in 1–6 hours, diarrhoeal type causes diarrhoea in 8–16 hours.
- Staphylococcus aureus: the cook's bandaged finger and no gloves; vomiting typically within 1–6 hours.
Distinguishing evidence:
- Laboratory: stool and vomit culture; food samples showing B. cereus at ≥10⁵ cfu/g; S. aureus and staphylococcal enterotoxin in curd rice or a swab from the cook's finger; phage typing or molecular typing to link the cook's isolate to the food.
- Interview/epidemiology: attack rate by food item-who ate curd rice versus only pulao; onset times; a cluster of early vomiting among guests served by the affected cook.
Without lab results, do not name one organism as confirmed. Both hypotheses should guide immediate action.
3. List the immediate corrective actions and the CCPs to include in the HACCP plan for the next event.
Read the worked answer
Immediate actions: stop serving and discard all leftovers; exclude the cook with the infected finger from food handling until a doctor clears him; provide soap, running water and disposable gloves; use boiled or treated water; clean and sanitise the service hall and utensils; report to the food safety authority and cooperate with sampling; keep all remaining food for testing.
HACCP CCPs:
- Cooking: rice and curd rice to >90°C.
- Cooling: if not served immediately, cool rapidly to <5°C within 2 hours.
- Hot-holding: >60°C; limit ambient service to 2 hours.
- Reheating: once to >74°C.
- Handler hygiene: exclude infected handlers; hand-wash stations with soap.
- Water: potable water testing and treatment.
Records: cooking and holding temperatures every 30 minutes, handler health log, water test reports, and guest complaint log.