1. Assistant Professor, Department of Medical Microbiology and Immunology, College of Medicine, Texas A & M University, College Station, Texas 77843.
2. Assistant Professor, Department of Pediatrics, Universidad del Valle, Cali, Colombia.
3. Department of Population and Nutrition Projects, World Bank, Washington, D.C.
4. Assistant Professor, Department of Microbiology, Indiana University School of Medicine, Indianapolis, Indiana 46202.