1. From the University of Texas Health Science Center at Houston (J.S., T.P.), Houston, TX; Department of Epidemiology (D.N.), Johns Hopkins Bloomberg School of Public Health, Baltimore, MD; Seattle Children's Hospital (J.T.F.), Seattle, WA; Cincinnati Children's Hospital Medical Center (M.M.), Cincinnati, OH; Children's Mercy Hospital (B.A.W.), Kansas City, MO; Children's Hospital of Philadelphia (S.F.), Philadelphia, PA.