1. Department of Pathology and Microbiology, College of Medicine, University of Nebraska Medical Center, Omaha, NE 68198, USA
2. Department of Internal Medicine, College of Medicine, University of Nebraska Medical Center, Omaha, NE 68198, USA
3. Department of Environmental, Agricultural & Occupational Health, College of Public Health, University of Nebraska Medical Center, Omaha, NE 68198, USA
4. Veterans Affairs Nebraska-Western Iowa Health Care System, Omaha, NE 68105, USA