From the Department of Occupational and Environmental Health, College of Public Health (Drs Mikulski, Sprince, and Fuortes), Department of Internal Medicine (Dr Gerke), Department of Biostatistics, College of Public Health (Mr Lourens), and Roy J. and Lucille Carver College of Medicine (Mr Czeczok), The University of Iowa, Iowa City; and Surveillance Branch (Dr Laney), Division of Respiratory Disease Studies, National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention, Morgantown, WVa .