Quantitative Risk Assessment for Campylobacteriosis in New Zealand by the Bayesian Approach

Introduction: New Zealand has the highest rate of reported campylobacteriosis in the developed world. Due to the large economic and health consequences of campylobacteriosis, intervention programs to reduce the disease rates are required to be designed and implemented. Quantitative microbial risk assessments (QMRA) are used to identify all the risk pathways in the food chain and to examine the most effective interventions to reduce the rate of foodborne illness. Many of these risk assessment studies have been conducted using the infeasible Monte Carlo approach.

Purpose: The purpose of this study was to conduct a QMRA by Bayesian inference using a Bayesian Belief Network model, which has many advantages.

Methods: A simplified model was used to describe the entire food chain from farm to fork with all the variates, parameters and variables of interest. The microbiological data of two New Zealand poultry processing plants for the last two years were incorporated. Numerical computations were performed using WinBugs software.

Results: The QMRA indicated that hygiene has a significant impact on the total probability of illness. An increase in the poor hygiene percentage by approximately 50% reflected an increase of approximately 50% in the probability of developing illness; the impact of increasing the contamination prevalence on farms and after plant processing was similar to the hygiene impact. However, the estimated probability of contracting campylobacteriosis by consuming poultry predicted 2,000 more cases than the actual notified number from all the sources. This is a more plausible estimate than the QMRA estimate which used the Monte Carlo method, given the number of unreported cases and the number of campylobacteriosis cases acquired by sources other than poultry consumption.

Significance: The results of this study provide an attractive and reliable tool for risk management in selecting the best and most effective intervention (e.g. education of consumers) for reducing campylobacteriosis, given the impossibility of producing Campylobacter-free chicken under the current chemical interventions applied at processing plants.