1. From the Divisions of Infectious Diseases (TSS) and Gastroenterology and Nutrition (CD, LB, and LF), Children's Hospital, Harvard Medical School, Boston, MA; the Division of Pediatric Clinical Research, Department of Pediatrics, Miller School of Medicine, University of Miami, Miami, FL (DDK and TLM); the Divisions of Infectious Disease (GAW) and Gastroenterology (JN), Golisano Children's Hospital