Food Poisoning Outbreak in a Hostel Mess - Park's PSM Answer

PART 1 - Probable Cause of Such Illness (3 Marks)

"An acute gastroenteritis caused by ingestion of food or drink contaminated with either living bacteria or their toxins or inorganic chemical substances and poisons derived from plants and animals."

1. History of ingestion of a common food (hostel mess)
2. Attack of many persons at the same time (50 students simultaneously)
3. Similarity of signs and symptoms in the majority of cases

Most Probable Causes in a Hostel/Community Feeding Setting:

• Chemical contamination - pesticides, heavy metals (cadmium, mercury, arsenic)
• Naturally occurring toxins in plants or seafood

PART 2 - Investigation of the Outbreak (10 Marks)

Step 1 - Verify the Diagnosis and Define the Outbreak

• Confirm that the illness is indeed food poisoning by reviewing clinical features
• Establish that a cluster of cases occurred following a common meal
• Prepare an epidemic curve (time of onset vs. number of cases) to estimate incubation period
• Calculate the attack rate = (Number who ate and fell sick / Total who ate) x 100

Step 2 - Secure a Complete List of People Involved and Their History

"All the people who have shared part of the food should be interviewed. They may be supplied questionnaires concerning the foods eaten during the previous 2 days, and place of consumption; time of onset of symptoms; symptoms of illness (nausea, vomiting, diarrhoea, abdominal pain, headache, fever, prostration, etc.) in order of occurrence; personal data such as age, sex, residence, occupation, and any other helpful information."

• Questionnaires should also be administered to kitchen employees and food handlers
• Identify who ate what - food-specific attack rates help pinpoint the vehicle

Step 3 - Identify the Suspected Food (Vehicle of Infection)

• Calculate food-specific attack rates: attack rate among those who ate a specific food vs. those who did not
• The food with the highest attack rate among those who ate it, and lowest among those who did not, is the incriminated food
• Common vehicles in a hostel mess: rice, curries, dal, meat dishes, milk/curd, chutneys

Step 4 - Laboratory Investigations

• Stool samples from all affected students - bacteriological culture (aerobic and anaerobic)
• Vomit samples from affected students
• Remnants of suspected food - examine aerobically and anaerobically
  • To incriminate the causative agent
  • To determine the total bacterial count and relative numbers of each kind (indicates degree of contamination)
• Stool samples of kitchen employees and food handlers - to identify carriers
• Phage typing of isolated organisms for complete laboratory identification
• If botulism suspected: animal experiments - feed rhesus monkeys with food remnants; perform protection tests (inject saline filtrate of food subcutaneously in mice, protect some with antitoxin)

Step 5 - Inspect Kitchen, Mess, and Food Storage

• Visit and inspect the hostel kitchen and mess area
• Check for:
  • Temperature control of food storage (refrigeration)
  • Food preparation practices - reheating, time-temperature abuse
  • Personal hygiene of food handlers (skin infections, nasal/throat infections)
  • Sources of water supply and its sanitation
  • Disposal of kitchen waste
  • Pest control (rats, mice, cockroaches - can contaminate food)
  • Crockery and utensil cleanliness

Step 6 - Establish the Source and Mode of Contamination

• Identify the index case among kitchen staff if possible
• Determine whether contamination occurred at:
  • Source (raw material - infected animals/poultry)
  • During preparation (food handler with S. aureus infection)
  • During storage (improper refrigeration allowing bacterial multiplication)
  • During service (cross-contamination)

Step 7 - Reporting

• Notify the health authorities (Medical Officer of Health/Chief Medical Officer)
• Submit a formal report including:
  • Total number of cases, attack rate
  • Incriminated food
  • Causative organism
  • Source and mode of contamination
  • Recommendations

PART 3 - Prevention and Control (7 Marks)

A. Control of Bacteria in Food (Source Control)

1. Infected animals: Strict veterinary supervision of slaughterhouses and dairy farms; sick animals should not be slaughtered for food; milk from cows with mastitis should not be used
2. Food handlers: Regular medical examination and bacteriological testing of all kitchen staff and food handlers; those with boils, skin infections, sore throat, or diarrhoea must be excluded from food handling duties
3. Rodent and pest control: Rats and mice are heavily infected with Salmonella and contaminate foodstuffs via urine and faeces; regular deratting and pest control in kitchen and store rooms is essential

B. Prevention of Bacterial Multiplication in Food (Key Principle)

1. Temperature control - the most important measure: Bacteria multiply rapidly between 10°C and 60°C ("danger zone"). Prevention requires:
   • Keep cold foods below 5°C (refrigeration)
   • Keep hot foods above 60°C
   • Do not leave cooked food at room temperature for more than 2 hours
   • Bulk-cooked food in hostel should be consumed the same day; leftover food must be rapidly cooled and refrigerated
2. Proper cooking: Thorough cooking kills vegetative bacteria; all meat, poultry and egg dishes must be cooked to an internal temperature of at least 74°C
3. Avoid reheating food repeatedly: Reheated food, especially meats and rice, is a common cause of Cl. perfringens and Bacillus cereus poisoning
4. Safe water supply: Ensure potable water is available for food preparation and washing

C. Prevention of Cross-Contamination

1. Separate raw and cooked foods: Raw meat and poultry should be kept away from cooked or ready-to-eat food; separate cutting boards and utensils should be used
2. Clean and sanitize surfaces: Kitchen surfaces, equipment, and utensils must be regularly cleaned and disinfected
3. Personal hygiene of food handlers:
   • Hand washing with soap before handling food and after toilet use
   • Clean uniforms, hair nets, gloves
   • No handling of food with bare hands for ready-to-eat items

D. Education

1. Health education of kitchen staff, mess workers, and hostel management about:
   • Correct food storage temperatures
   • Proper cooking techniques
   • Personal hygiene
   • Early reporting of illness

E. Surveillance and Monitoring

1. Regular inspection of the hostel mess by public health authorities
2. Food safety audits - periodic microbiological testing of food samples from the mess
3. Early reporting system: Students and staff should be encouraged to report any illness promptly so outbreaks can be detected and investigated quickly

F. Immediate Control Measures During an Outbreak

• Stop serving the suspected food immediately
• Treat affected students: Oral rehydration therapy (ORS) for mild-moderate dehydration; IV fluids for severe cases; specific antibiotics only if indicated (e.g., Salmonella with systemic features)
• Isolate and treat severely ill students
• Quarantine the mess kitchen pending investigation
• Disinfect implicated utensils, surfaces, and storage containers