Épidémiologie spatiale de la campylobactériose au Québec

Campylobacteriosis is a leading cause of acute bacterial gastro-enteritis in industrialized countries. The epidemiology of the disease is complex, involving many sources and transmission pathways. The principal objective of this project was to study environmental factors and methodological aspects pertinent to the spatial epidemiology of human campylobacteriosis using cases reported in Quebec (Canada) between 1996 and 2006.  A conceptual diagram of sources and transmission pathways of Campylobacter was first proposed following a synthesis of current epidemiological knowledge based on a comprehensive literature review. The risk of recurrent episodes in relation to patient characteristics was described. Life table estimates and logistic regression were used for modeling. Compared to campylobacteriosis risk in the general population, the risk for a recurrent disease event was higher for a period of four years with a decreasing trend. This increased risk was similar across gender but higher for people from rural areas and lower for children under four years old. These results may suggest the absence of durable immunity or clinical resilience following a first episode and/or periodic re-exposure, at least among reported cases. Next, criteria were proposed and applied to ascertain the best geographical unit to use. Nine measurable criteria were proposed, including biological relevance, communicability of results, ease of data access, distribution of exposure variables, cases and population, and unit shape. These criteria were applied to various geographical units derived from administrative, health services and natural frameworks. Ultimately, the municipal geographical unit performed the best, given the specific objectives of the study. Future research areas for optimizing the choice of geographical unit were discussed.  Another objective was to estimate and compare the associations between incidence and various environmental characteristics (poultry density, ruminant density, slaughterhouse, temperature, and precipitation) and demographic characteristics (population density, diploma) using seven different geographical units. Conditional autoregressive models were used for statistical modeling. In general, the number of significant predictors decreased as the aggregation level increased but directions of associations were consistent. More aggregated scales tended to show larger but more variable estimates for all variables, with the exception of the presence of slaughterhouses. This study highlighted the need for careful selection and analysis of geographical units when using ecological designs in epidemiological studies. Finally, the association between environmental characteristics and incidence in relation to four age groups and deux seasonal periods was studied. A multi-level Poisson regression model was used for modeling at the municipal level. High ruminant density was positively associated with incidence but decreased with age. High poultry density and presence of a large poultry slaughterhouse were also associated with higher incidence for people aged 16-34. Associations were also detected with population density and average daily precipitation. Except for population density, associations were constant across seasonal periods. Close contact with farm animals is most likely involved in the associations observed. Clearly, age and season must be considered in future studies on campylobacteriosis and in the design of preventive measures.

Keyphrases: Ruminant, Campylobacteriosis, Ecological study, Geographical unit, Poultry, Recurrent episode, Ruminant, Spatial epidemiology, Quebec