1. Department of Environmental, Agricultural & Occupational Health, University of Nebraska Medical Center, Omaha, Nebraska
2. Department of Environmental Health, Indiana University School of Public Health, Bloomington, Indiana
3. Department of Internal Medicine, Division of Infectious Diseases, University of Nebraska Medical Center, Omaha, Nebraska
4. Department of Pathology and Microbiology, College of Medicine, University of Nebraska Medical Center, Omaha, Nebraska
5. Nebraska Public Health Laboratory, Omaha, Nebraska
6. Department of Biostatistics, University of Nebraska Medical Center, Omaha, Nebraska