Objective: To determine long-term predictors of bronchial hyperresponsiveness (BHR) and forced expiratory volume in one second (FEV1) decline.
Methods: A longitudinal study in 110 bakers in 4 industrial bakeries and 38 non-exposed workers was conducted at the workplace with a mean of 3.3 visits per subject over a period of 13 years and a mean duration of follow-up of 6 years in bakers and 8 years in non-exposed subjects. A respiratory health questionnaire was administered; occupational allergen skin prick tests, spirometry and a methacholine bronchial challenge test were performed at each visit. In each bakery, full-shift dust samples of the inhalable fraction were obtained in order to assess the exposure of each job assignment. The repeated measurements of BHR and FEV1 were analyzed using mixed effects logistic and linear regression models in subjects seen at least twice.
Results: BHR, respiratory symptoms and their simultaneous occurrence depended on the duration of exposure. FEV1 significantly decreased with duration of exposure and BHR at a preceding visit. This result persisted when adjusting for the effect of BHR at the current visit. The measured exposure levels were not a significant predictor for any outcome. Occupational sensitization was only a predictor of a decline in FEV1 when duration of exposure was not included.
Conclusion: In flour-exposed industrial bakers, length of exposure and smoking are long-term determinants of BHR and of the decrease in FEV1. BHR at a preceding visit predicted lower FEV1 even when accounting for the effect of BHR at the current visit.
Keywords: Bakers; Bronchial hyperresponsiveness; Epidemiology; Longitudinal study; Lung function; Occupational exposure.