1. Section of Pediatric Tropical Medicine, Baylor College of Medicine, National School of Tropical Medicine, Houston, Texas.
2. School of Public Health, University of Texas Health Science Center at Houston, Houston, Texas.
3. Section of Immunology, Department of Pediatrics, Baylor College of Medicine, National School of Tropical Medicine, Houston, Texas.
4. Medical School, University of Texas Health Science Center at Houston, Houston, Texas.