1. Division of Environmental and Occupational Health Sciences, National Jewish Health, Denver, Colorado
2. Department of Medicine, University of Colorado School of Medicine, Aurora, Colorado
3. Division of Pulmonary, Allergy, Critical Care and Sleep Medicine, and
4. College of Public Health, Ohio State University, Wexner Medical Center, Columbus, Ohio; and
5. Division of Lung Diseases, National Heart, Lung, and Blood Institute, Bethesda, Maryland