Campylobacteriosis in New Zealand: Causes and control : A thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Lincoln University

Abstract

New Zealand (NZ) has a higher rate of reported campylobacteriosis cases than the rest of the developed world. The majority of human campylobacteriosis cases are attributable to the consumption of poultry products. The hypotheses explored in this study are: (i) NZ C. jejuni strains have a greater heat tolerance and hence are better able to survive cooking, (ii) NZ strains are more oxygen tolerant, (iii) secondary poultry processing practices increase the NZ chicken contamination with Campylobacter (iv) Food preparation home hygiene practices in NZ are poor compared with the developed world. Quantitative microbial risk assessment (QMRA) was carried out by applying an advanced Bayesian approach to assess all the factors in the food chain, which impact the final campylobacteriosis risk estimation. Moreover, the current intervention practices applied at the poultry plant was investigated to find a better physical intervention method than the potential unsafe chemical intervention processes applied currently. Finally, an alternative approach to QMRA that could predict more accurately the annual campylobacteriosis risk in NZ was also investigated. The kinetic parameters (D and z values) determined under the isothermal and dynamic condition in broths culture or on chicken skin for the most implicated strains in human campylobacteriosis cases in New Zealand were broadly in agreement with published international data. They did not indicate that NZ strains (ST 474, ST 190, ST 48, ST 45 from humans and poultry) were more heat resistant than the overseas strains. Similarly, the bacterial survival under oxidative stress showed that the oxygen tolerance of NZ strains was also similar to other internationally reported strains. A secondary practice (marination of chicken by needle injection) investigated at a poultry production plant did not significantly increase the chicken carcasses contamination level. The results confirm that the tested New Zealand C. jejuni strains do not have unusual characteristics, and the high rate of campylobacteriosis in New Zealand is not associated with the emergence of more environmental stress-resistant strains. This finding has a significant impact on the poultry industry, regulators, consumers and researchers as it confirms the scientific evidence to maintain the stipulated standards for the heat treatment practices at poultry plants, food services and at homes. Changes to heat treatment practices can cause unpredicted loss to the poultry industry. It is important for the regulatory bodies to convey to all consumers, the critical message of the cooking temperature given the reluctance of NZ consumers to use food thermometers to verify the home cooking temperatures. The results of the consumers' food handling practices survey revealed that the mean score of food safety practices and food safety awareness of the New Zealanders who participated in the survey was below the average questionnaire score of 10.5 out of 21 (the total score ). The study confirmed that the awareness of basic food hygiene and safe food preparation practised by people in New Zealander was lower than in other developed countries. Therefore, an innovative and more effective approach needs to be implemented for future consumer education strategy. The QMRA conducted in this study indicated that hygiene has a significant impact on total illness probability. The 'Bayesian hierarchal model', which provides a better insight into the food chain than the 'time series model' and is more informative as it incorporates all the factors that impact on the final risk estimation. The QMRA model was able to identify the consumer hygiene practices, the initial contamination prevalence at the farm and the practices at the processing plant, as the significant factors influencing the final risk estimate. The association between the reduction in birds/chicken carcases prevalence and improvement in home hygiene practice and the calculated reduction in risk of human disease was estimated to be 1:1, which agrees with international findings. Thus, QMRA model can easily determine the impact of any intervention in the food chain. Therefore, the effect of a new planned intervention such as consumer education on the final risk estimate should be clear for the policymakers, risk managers and health professionals. This can be achieved by altering the priors of the consumer hygiene practices in QMRA model. Similarly, other interventions at poultry plants and farms should also be assessed by altering the priors of farms and poultry plants. The Bayesian hierarchal model, which has been used in this study, was able to deliver the expected outcomes and to provide a fast response for policymakers and risk managers. The Auto-Regressive Integrated Moving Average (ARIMA) with an intervention model provided one of the best prediction of the annual campylobacteriosis risk in NZ from the ten models tested. ARIMA intervention model has the lowest forecast error with, only 9 % campylobacteriosis cases more than the actual notified cases. The Holt-Winters method, being local in nature, quickly adapts to the new post-intervention regime and also gives a good prediction which is comparable with the ARIMA intervention models. This method has the additional advantage that it is simple to calculate. This study also highlighted the potential alternative physical interventions such as the immersion in hot water or hot water wash at poultry processing plants that could be employed with possible another physical intervention in case a ban on chemicals that are currently used to control campylobacteriosis is imposed in NZ