Full length articleComparison of three modelling approaches to predict the risk of campylobacteriosis in New Zealand
Introduction
Risk assessment (RA) in food is a scientifically based process of identifying and characterising the hazards and risk factors associated with a given food system. Thus, microbial risk assessment (MRA) is the scientific evaluation of known or potential adverse health effects resulting from human exposure to biological hazards. This approach employs mathematical models that are used to predict: (i) the introduction of pathogens into food, (ii) the replication of pathogens in food over time, (iii) the destruction of pathogens by heat treatment or other techniques, (iv) the consumption of pathogens in food and (v) the subsequent probability of illness. New Zealand has a high rate of reported campylobacteriosis cases, especially when compared with other developed countries (Baker et al., 2006). Therefore, predicting campylobacteriosis cases has become a matter of considerable concern in New Zealand. Moreover, the intervention strategies selected by policymakers can be evaluated by the cost and benefit in terms of the number of campylobacteriosis cases which are expected to be prevented. Therefore, there is a need to develop a model to accurately predict accurately the number of campylobacteriosis cases in New Zealand. Time series forecasting methods have been successfully applied in the fields of engineering, science, sociology and economics (Brockwell and Davis, 2002). The classical time series modelling approach is considered as an appropriate technique to predict campylobacteriosis in New Zealand (Weisent et al., 2010). The objective of this study is to investigate which modelling technique can provide a suitable model to accurately predict the number of campylobacteriosis cases in New Zealand, to list the pros and cons of each modelling approach and to explore possible risk factors for the disease. Previously, Parsons et al. (2005) compared three modelling approaches for the QMRA, and others (Smid et al., 2010) compared two approaches for the QMRA or others introduced the fuzzy model (Davidson et al., 2006) but none of these studies has included the time series method for predicting risk.
Section snippets
2.1. QMRA approach description
The concentration of the pathogen is the variable which each quantitative microbial risk assessment (QMRA) will quantify in order to follow the dynamics of the pathogen through the food chain. The concentration of the pathogen is usually dependent on the variable describing the concentration at a previous stage in the food chain and other process parameters, such as temperature, time, pH, water activity etc. Generally, the QMRA divides the food chain into a specific number of modules which can
3.1. Bayesian techniques
The statistical output of the prior distribution and posterior distribution were summarized in Table 3. The Monte Carlo error (MC error) for each parameter is also shown in the table. The MC error assesses the accuracy of the posterior estimates. It represents the difference between the mean of the sampled values, which are used as the estimate of the posterior mean for each parameter, and the true posterior mean. The statistics table also reports the sample standard deviation (sd) with the
Conclusion
The complete food chain has been modelled by a Bayesian hierarchal model, which provides better insight than the time series model into the food chain and is more informative as it incorporates all the factors that impact the final risk estimation. Thus, it can easily determine the impact of any intervention in the food chain. Therefore, the effect of a new planned intervention such as a consumer education plan was clear for the policy makers, risk managers and health professionals before the
Acknowledgement
The author would like to thank Professor Geoff Jones from the Institute of Fundamental Science, Massey University for his statistical support. The author greatly acknowledges the provision of data by The Poultry Industry Association of New Zealand (PIANZ) and the author appreciates the support of Michael Brooks, executive director, and Kerry Mulqueen from The Poultry Industry Association of New Zealand. Dr. Roy Biggs, Q.A Manager at Tegel Foods Ltd, and Don Thomas, Manager of Poultry Research
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Present address: Lincoln University, Faculty of Agriculture and Life Sciences PO Box 85084, Lincoln 7647, Christchurch, New Zealand.