Amélioration de l’évaluation de l’exposition professionnelle rétrospective dans les études épidémiologiques à base populationnelle

Retrospective occupational exposure assessment forms a critical and challenging component of population-based case-control studies that requires estimating lifetime exposures for each subject with high accuracy and limited information. In the 1980s, researchers in Montreal developed a novel method involving the expert review of detailed job histories to evaluate exposure to some 300 agents, which was applied to 4 large case-control studies of cancer in the Montreal region between 1979 and 2005. The data collected by the group represents a unique body of knowledge on retrospective occupational exposures that could inform the exposure assessment of new studies. The objective of this thesis was to develop and examine approaches designed to improve retrospective exposure assessment in population studies by building on the information contained in the Montreal group database. The first component involved the development of CANJEM, a job-exposure matrix (JEM) summarizing the exposure data for 258 agents across 31,673 jobs spanning 1930-2005. CANJEM featured 3 axes: agents, occupation or industry (in 7 classification schemes, each in multiple resolutions) and periods (1, 2 or 4 categories). Each cell depicts the exposure profile of jobs using 5 indices: probability of exposure (percentage), reliability, intensity and frequency (as relative distributions of ordinal ratings) and frequency-weighted intensity (FWI; continuous). Over 90% of the Canadian working population were covered by CANJEM cells according to 2 national surveys (1986 and 2011).  The second component aimed at refining the CANJEM estimates for 5 agents by applying Bayesian hierarchical models to pool information on exposure among cells from similar occupations, while also accounting for the source studies of jobs. The estimates of cells based on fewer than 5 jobs were often overly sensitive to the influence of the other occupations, whereas their influence ranged from moderate to negligible for cells based on 5 or more jobs. The third comportment aimed to develop quantitative estimates of wood dust exposure for CANJEM cells by modelling 5170 historical (1981-2003) measurements from the Canadian Workplace Exposure Database. Predicted geometric mean (GM) concentrations of cells for 8 hours, breathing zone and year 1989 ranged 0.49–1.67 mg/m3, with contrasts of 1-1.3-2.3 in the GMs between the low, medium and high intensity ratings. The model provided estimates of wood dust concentrations for any cell with some exposure in CANJEM. The last component aimed to compare the exposures assigned with a novel hybrid approach combining expert assessment and job-exposure profiles summarizing past evaluations by occupation, to the traditional expert method. The comparisons of the exposure data covering 203 agents and 90 occupations showed a higher reliability in the assessments as rated by the experts with the hybrid method. A decrease in the within-occupation variability of the exposures assigned with the hybrid method was also found, which may be explained by a greater consistency in the assessments and by the application of the job-exposure profiles. The use of the Montreal group database provided a backbone for developing and refining a multidimensional JEM, such as with the development of quantitative estimates. CANJEM represents a unique resource that could be applied to assess and prevent occupational diseases in Canada and elsewhere. The assessment of the hybrid expert approach also documented the usefulness of available exposure data to inform the process of exposure assessment. The set of methods developed in this project could also be applied to other retrospective exposure assessment databases.

Keyphrases: Occupational exposure, Exposure assessment, Job-exposure matrix, Case-control studies, Population studies, Retrospective studies