1. From the Food and Drug Administration, Center for Drug Evaluation and Research, Office of Pharmacovigilance and Epidemiology, Division of Epidemiology (S.T.B., K.G., C.W., P.G, C.M), Office of New Drugs, Division of Pediatric and Maternal Health (L.S., E.R., T.J.), and Division of Medical Imaging Products (K.B.B, I.K), 10903 New Hampshire Ave, Silver Spring, MD 20903; and Harvard Medical School and Harvard Pilgrim Health Care, Boston, Mass (E.F., M.S.).