B01015: Determining exposure assessment and modelling risks associated with the preparation of poultry products in institutional catering and the home

Study Duration: June 1999 to June 2001

Contractor: University of Wales Institute, Cardiff

Poultry has been implicated as a major source of potential pathogens such as campylobacter and salmonella. Thus poultry should always be cooked adequately and handled appropriately to minimise cross contamination. Strategies to reduce food poisoning need to be developed based upon risk assessment. Risk assessment is concerned with determining the risk associated with a hazard and can be based on either quantitative (numerical) or qualitative (values such as high, medium or low) data.

Exposure assessment forms part of the risk assessment approach and requires information on how much of the pathogen is present in the raw food, circumstances under which the food is prepared and consumption patterns (e.g. portion size). Exposure assessment estimates how likely it is that an individual or a population will be exposed to a hazard and what level of the pathogen is likely to be ingested. The credibility of this type of microbial risk assessment is based upon its ability to take into account the variability and uncertainty of each parameter implied in the estimation of final risk. One of the greatest areas of variability and uncertainty relates to exposure assessment and varying hygiene practices in food service establishments and the home.

The aim of this project was to provide data on exposure assessment that can be used to identify optimum food handling strategies.

There will be three phases to this project.

Phase 1: Raw products

• Determine the extent of contamination of raw chicken and associated packaging obtained from supermarkets and butchers� shops
• Enumeration of micro-organisms on the surface of chicken and the number transferred to hand contact surfaces within the kitchen for quantitative risk assessment

Phase 2: Consumer and catering establishment meal preparation

• Recruitment of consumers to prepare chicken meals (stir-fry and BBQs); visits to catering establishments when preparing chicken meals to observe adequacy of cooking
• Observations of practices used during meal preparation
• Determine the extent of contamination of surfaces with pathogens
• Determine the extent of contamination of raw, cooked and ready-to-eat foods

Phase 3: Exposure assessment

Development of mathematical modelling techniques:

• Modelling contamination events using event trees
• Development of a predictive dose model using probabilistic modelling.

Raw Products

Campylobacter and salmonella were isolated from 68% and 29% of retail chicken respectively. Campylobacter was isolated from the outside of chicken packaging (3%) and from whole packaging, which includes outside and inside, (34%), whereas salmonella was isolated from whole packaging only (11%). A high level of campylobacter was enumerated from chicken skin (mean of 7.4x10⁴ cfu g^-1 of skin), whilst a low level of salmonella (mean 30 cfu g^-1 of skin) was present. The average transfer rate of campylobacter from raw chicken to surfaces was 10% and the organism could still be recovered after touching eight consecutive surfaces.

Preparation of chicken meals by consumer

Overall 8% of the cooked chicken samples were contaminated with campylobacter, whilst 7% of ready-to-eat food items served with the meals (salad) and other cooked ingredients within the meal were contaminated. Salmonella was not detected. Assessment of contact surfaces indicated that no surfaces tested were positive for salmonella. However, various surfaces were contaminated with campylobacter, e.g. cupboard handles (20%), bin lids (5%), hot taps (5%), work surfaces (20%), etc. CHEF tests (enzyme tests) showed that 83% of chicken was adequately cooked by consumers, although stir-fry and barbecuing methods are most likely to result in inadequate cooking.

Preparation of chicken meals by catering establishment

All chickens were shown to be adequately cooked using the CHEF test. Overall 6% of the cooked chickens were contaminated with campylobacter, whilst 8% of ready-to-eat foods served with the meals were contaminated. No salmonella was detected. Assessment of the contact surfaces indicated that campylobacter contamination occurred on various surfaces, e.g. hot taps (10%), sinks (12%), chopping boards (6%), chefs� cloths (6%) and refrigerator handles (2%), whilst salmonella contamination occurred on the surface of sinks (2%), chefs' cloths (2%) and refrigerator handles (2%).

This project indicates high levels of contamination of raw chicken with campylobacter and lower levels of contamination with salmonella. Undercooking of chicken was only observed during consumer food preparation (BBQ and stir-fry meals). Micro-organsims could spread within the kitchen environment during the preparation of chicken meals within the domestic and catering kitchens. Observational and microbiological results showed that, in some instances, this could lead to contamination of cooked and ready-to-eat foods.

Collection of these data enabled a preliminary exposure assessment to be made by the design and development of mathematical modelling techniques. In particular the use of event tree and probabilistic modelling techniques has provided the first attempt at modelling cross contamination events within the domestic and catering kitchen. The method can be used to predict contamination rates in foods, and the effect of altering parameters on the overall rates of contamination can be explored. This project has resulted in a model which, after further development, may be used as a tool in the decision making and management of food safety.

The final report is available from the FSA Library and Information centre. To obtain a copy, please contact the Enquiry Desk,
Dr Elsie Widdowson Library and Information Services, Food Standards Agency (tel: 020 7276 8181/8182) or email: library&info@foodstandards.gsi.gov.uk).

Contact: For any enquiries concerning this research project, please contact the relevant Programme contact or email science@foodstandards.gsi.gov.uk