Longitudinal evaluation of dose-response relationships for environmental exposures and pulmonary function in swine production workers.

Studies describing respiratory health hazards for workers in swine production facilities have been published in the United States, Sweden, Canada, the Netherlands, and Denmark. Up to 50% of these workers experience bronchitis, organic dust toxic syndrome, hyper-reactive airways disease, chronic mucous membrane irritation, and other respiratory effects. These studies clearly point to the fact that this occupational environment poses a significant health risk hazard, and that control methods are needed to protect the worker. Before precise control strategies can be developed, implemented, and evaluated, dose-response studies are required to determine acceptable target levels for exposure. A previous manuscript described the development of multiple regression equations characterizing the relationships between environmental exposures and pulmonary response in a cohort of 207 swine producers. Baseline pulmonary function was included as a significant predictor of cross-shift decrements in pulmonary function in addition to personal measurements of dust, endotoxin, and ammonia concentrations. These equations were then used to predict specific exposure levels of dust and ammonia that could be expected to elicit significant decrements in cross-shift pulmonary function. This paper presents the results from analysis of follow-up data obtained on this same cohort 2 years after the initial measurements. At the second measurement period of the study (time-2), swine workers were found to have a mean cross-shift decrease in FEV1 of 2%. Cross-shift change in FEV1 was significantly correlated with personal exposures to total dust, total endotoxin, respirable endotoxin, and ammonia. The magnitude of the decrease in FEV1 was associated with increasing airborne concentrations of these environmental parameters thus confirming the dose-response relationship observed in the initial study (time-1). The correlation of dust with FEV1 changes in workers with more than 6 years of exposure (time-1 data) and more than 10 years of exposure (time-2 data) suggests that dust exposure is an important factor in chronic respiratory disease. Additionally, the correlation of endotoxins with FEV1 changes in the group with less than 6 years exposure (time-2 data) suggests endotoxins may have more significance for subacute respiratory effects. The agreement between observed cross-shift FEV1 changes measured in time-2 with changes predicted using regression equations derived from time-1 data demonstrates a consistent dose-response relationship over time for this cohort of swine production workers. This finding provides further support for conclusions of the previous study that levels of 2.5 mg/m3 (total dust) and 7.5 ppm (ammonia) are reasonable guidelines for occupational exposure limits in this environment.