1. Environmental and Occupational Health, Drexel University School of Public Health, Philadelphia, Pennsylvania 19102;
2. Southeast Center for Agricultural Health and Injury Prevention, University of Kentucky College of Medicine, Lexington, Kentucky 40504;
3. National Farm Medicine Center, Marshfield Clinic, 1000 North Oak Avenue, Marshfield, Wisconsin 54449;
4. National Farm Medical Center, 4270 29th Street, NE, Heimdal, North Dakota 58341;