Estimation and Validation of Flour Exposure in Bakeries in Alberta, Canada

Objectives: In epidemiological studies of work-related ill-health only current exposures can, at best, be measured. Previous exposures may be estimated using contemporaneous hygiene records or published data. This study aimed to create a job exposure matrix for exposure in bakers for use in an ongoing cohort study. Methods: A systematic review was conducted of English language publications on exposures in bakeries. All publications that appeared to contain quantitative measures of exposure to flour dust, wheat allergen, or fungal alpha-amylase were read independently by two investigators and relevant data extracted. A third investigator reviewed these data and publications were retained that reported full-shift exposures to inhalable dust, wheat allergen, or alpha-amylase, and for which geometric means (GMs) were given or could be estimated. For each study, the number of sampling results contributing to each GM was recorded together with information on task, bakery size, product, filter type, sampling head, the country in which the study was conducted, and the estimated year of sampling. Multivariable models were elaborated for each exposure using a linear mixed effects approach. The predictive capacity of the model for inhaled particles was tested against samples collected in eight Alberta bakeries. The capacity of exposure intensity, estimated from each of the three models, to predict sensitization was tested against skin prick testing (SPT) for bakery allergens in bakers currently employed in Alberta. Results: One thousand three hundred and ninety-seven publications were identified through the systematic search, of which 27 had data used to create one or more of the predictive models. Weighted GMs were used as outcome variables. For inhalable dust, task, bakery size, type of sampling head, and year of sampling contributed to the final model. For wheat allergen and alpha-amylase, task, bakery size, sampling head, and year of sampling again contributed. Product (bread rather than confectionary or mixed products) was also important in these two latter measures. The model for inhalable dust was used to predict the concentration in 33 samples from Alberta bakeries. Overall, 91% of observed samples had 95% confidence intervals (CIs) overlapping the 95% CIs of the predicted values. A model including the Alberta samples found no effect attributable to Alberta provenance. Using this model for inhalable dust and the models developed solely from the literature for wheat allergen and alpha-amylase, a positive SPT for bakery allergens in 57 bakers recruited for this study was significantly related to log cumulative exposure for each of the three outcome variables and to log exposure intensity for wheat allergen and alpha-amylase. Conclusions: The exposure models developed from the literature provide useful estimates of exposure. Calibration of the models against locally collected samples may be useful for countries poorly represented in the modeling dataset.