Changes in sputum cell counts after exposure to occupational agents: What do they mean?

Background: Exposure to occupational agents can induce eosinophilic inflamm ation in subjects with occupational asthma (OA), It might also induce nonsp ecific changes in airway inflammation in subjects without OA, Objectives: We sought to investigate the changes in airway inflammation ind uced by exposure to occupational agents in subjects with and without OA and to determine which changes in sputum eosinophil numbers and bronchial resp onsiveness to methacholine should be regarded as clinically significant for predicting a 20% fall in FEV1. Methods: We performed specific inhalation challenges (SICs) in 3 groups of subjects: subjects reporting a history consistent with OA with a positive S IC response (n = 17); subjects reporting a history consistent with OA with a negative SIC response (n = 14); and asthmatic subjects without any histor y of OA (n = 10). Induced sputum and methacholine challenges were performed at the end of the control day and again at the end of the last day of expo sure; the last day of exposure was always performed in the laboratory. Results: There was an increase in median sputum eosinophil and neutrophil n umbers in subjects with positive SIC responses. Cell counts remained unchan ged after exposure in asthmatic subjects without OA, A combination of a gre ater than 0.26 10(6)/mL increase in sputum eosinophil numbers and a decreas e in the concentration of methacholine inducing a 20% fall in FEV1 of at le ast 1.8-fold compared with baseline values predicted a 20% fall in FEV1 in 96% (95% CI, 70%-99%) of patients. Conclusion: Exposure to occupational agents per se does not induce airway i nflammation. Changes in both sputum eosinophil counts and methacholine resp onsiveness are satisfactory predictors of a significant bronchial responsiv eness to occupational agents.