1. From the Departments of Pediatrics, Microbiology, and Biostatistics, University of Alabama School of Medicine, Birmingham; Department of Pediatrics, Stanford University School of Medicine, Palo Alto, California; Department of Pediatrics, University of California-Los Angeles, School of Medicine, Los Angeles; Department of Pediatrics, University of California-San Diego, School of Medicine, San Diego; Department of Pediatrics and Preventive Medicine, Emory University School of Medicine, Atlanta