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Determine exposure assessment & modelling risks associated with the preparation of poulty - catering & home
Project Code: B01015
Food Research and Consultancy Unit Cardiff School of Health Sciences UWIC
Harrison, W ; Griffith, C;
Food Chemical Risk Analysis, Brighton
To determine exposure assessment and model the risk associated with Campylobacter and Salmonella following the preparation and consumption of poultry products in the home and food service establishments.
1. Devise meals involving poultry products
2. Analyse, identify and catalogue practices contributing to pathogen contamination and / or
3. Design and develop modelling techniques using contamination and consumption data to survival with these foods, and correlate with microbiological data on foods and surfaces determine the probability of risk associated with the contaminated foods and identified practices.
4. Describe how the methods can be used to identify key factors affecting exposure risks and discuss the application of such information in risk management policy development.
Phase 1: Raw products
- Determining the extent of contamination of raw chicken and associated packaging obtained from supermarkets and butchers’ shops
- Enumeration of microorganisms 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 the 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 predictive dose modelling using probabilistic modelling
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 (includes outside and inside) (34%). Salmonella was isolated from whole packaging only (11%). A high level of Campylobacter (mean of 7.4 x 104 cfu g-1 of skin) was enumerated from chicken 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 consumers and within catering establishments CHEF tests showed 83% of chicken to be adequately cooked by consumers. Overall 8% of the cooked chicken were contaminated with Campylobacter whilst 7% of ready-to-eat food served with the meals (salad) and other cooked ingredients within the meal were contaminated. Salmonella was not detected. No surfaces tested were positive for Salmonella, however, various surfaces were contaminated with Campylobacter e.g. cupboard handles (20%), bin lid (5%), hot tap (5%), work surfaces (20%), tongs (handles).
All chicken was 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 overall. No Salmonella was detected. 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 sinks (2%), chefs cloths (2%) and refrigerator handles (2%).
The probability of specific food handling and preparation risks occurring during (a) consumer food preparation and (b) catering food preparation included the following:
- A 1 in 3.3 chance of failure to discard raw chicken packaging immediately after use
- A 1 in 4.3 chance of potential contamination of ready-to-eat foods
- A 1 in 5 chance of potential contamination of the cooked meal
- A 1 in 7.5 chance of adequate hand washing after handling raw chicken or packaging
- A 1 in 2.3 chance of failure to discard raw chicken packaging immediately after use
- A 1 in 5 chance of potential contamination of ready-to-eat foods
- A 1 in 12.5 chance of potential contamination of the cooked meal
- A 1 in 5 chance of adequate hand washing after handling raw chicken or packaging
- Results from microbiological and observational data enabled an event tree to be developed
- The event tree could be analysed to provide an assessment of the overall probability of positive outcomes (possible transfer of contamination from raw to finished foods) by adding together all probabilities associated with each positive end point. Overall outcomes could then be broken down to identify key factors.
- The overall probability of positive outcomes was higher for meals prepared in the domestic kitchen compared to catering establishments. The probability of transfer ranged from 9% in nursing homes to 65% in other institutions. When specific recipes were assessed, the probability of transfer ranged from 12% for roast chicken to 83% for grilled chicken.
- The most important factor affecting the probability of transfer of contamination to finished food was whether the raw food was contaminated. Inadequate cooking and hand washing appeared to be the most significant events leading to higher positive outcomes within domestic food preparation whilst inadequate hand washing and potential contamination of ready-to-eat food appeared to be the significant factors within catering food preparation. The preparation of ready-to-eat foods with the chicken appeared to be an important factor.
- Probabilistic modelling was able to take variability in contamination levels, transfer patterns and rates and food consumption into account and could be used to predict the probability that an individual in a given population would be subject to a level of exposure that might be associated with the potential for infection. Exposure models were developed for pre-school children, adults and the elderly. For the transfer of Campylobacter in catering situations, the highest exposure to Campylobacter in homecooked food are much higher for barbeques than for stir-fries. The probabilities of exposure to high levels of Campylobacter at barbeques were the highest observed.
- After raw contamination levels, the most important factor influencing exposure levels was the contamination transfer rates used in the model. This is an area where further work may be required.
- Exposure levels resulting from each of the scenarios studied can be compared with putative minimum infective doses for the different populations considered.
Technical Evaluation / Interpretation
This project indicates high levels of contamination of raw chicken with Campylobacter and lower levels of Salmonella. Undercooking of the chicken was only observed during consumer food preparation (BBQ and stir-fry meals). In addition the microorganisms could spread within the kitchen environment during the preparation of chicken meals within 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 determined by the design and development of mathematical modelling techniques. In particular the use of event tree and probabilistic modelling 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 can be explored. Most importantly this project has resulted in a model which after further development may be used as a tool for use in the decision making and management of food safety. The model may for instance be used to aid in the prioritisation of messages for food hygiene interventions for the food service industry and consumers.
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