1. Department of Biostatistics, College of Public Health and Health Professions, College of Medicine University of Florida Gainesville 32611 FL U.S.A.
2. Emerging Pathogens Institute University of Florida Gainesville 32611 FL U.S.A.
3. Department of Environmental and Global Health, College of Public Health and Health Professions University of Florida Gainesville 32611 FL U.S.A.