1. Groupe de Recherche sur les Maladies Infectieuses du Porc, Faculté de Médecine Vétérinaire, Université de Montréal, Saint-Hyacinthe, Québec, Canada J2S 7C61;
2. Division of Pediatric Infectious Diseases, University of California, San Diego, La Jolla, California 92093-06722;
3. Division of Infectious Diseases, Children's Hospital and Medical Center, Seattle, Washington 981053; and
4. Division of Infectious Diseases, Children's Hospital Los Angeles, Los Angeles, California 900274