1. From the Laboratory of Infectious Diseases, National Institutes of Health, Bethesda, MD, Department of Microbiology, Free University of Brussels, Belgium, and the Research Foundation of the Children's Hospital National Medical Center and Department of Child Health and Development, George Washington University School of Health Sciences, Washington, DC; Institute of Nutrition of Central America and Panama, Guatemala; University of Costa Rica, San Jose (address reprint requests to Dr. Yolken at the...