1. Division of Geographic Medicine, Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama 35294 and Program in Epidemiology of Infection and Immunity, Schools of Public Health and Medicine, University of Alabama at Birmingham, Birmingham, Alabama 35294
2. Division of Geographic Medicine, Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama 35294
3. Program in Epidemiology of Infection and Immunity, Schools of Public Health and Medicine, University of Alabama at Birmingham, Birmingham, Alabama 35294 and Department of Epidemiology and International Health, School of Public Health, University of Alabama at Birmingham, Birmingham, Alabama 35294
4. Children's Hospital of Philadelphia, Department of Pediatrics, University of Pennsylvania, Philadelphia, Pennsylvania 19104