From the Departments of Neurology (M.R.W., V.D., S.A.J., F.C.C., J.M.G.), Biochemistry and Biophysics (H.A.S., K.C.Z., J.L.D.), Laboratory Medicine (S.A., G.Y., S.F., D.S., B.B., B.H., S.M., C.Y.C.), and Epidemiology and Biostatistics (J.N.), the Department of Medicine, Division of Infectious Diseases (C.L., C.Y.C.), the Department of Medicine, Division of Hospital Medicine (A.B.), and Weill Institute for Neurosciences (M.R.W., V.D., S.A.J., F.C.C., J.M.G.), University of California, San Francisco (UCSF), UCSF-Abbott Viral Diagnostics and Discovery Center (S.A., G.Y., S.F., D.S., B.B., C.Y.C.), the Chan Zuckerberg Biohub (C.L., J.L.D.), and Zuckerberg San Francisco General Hospital (B.H.), San Francisco, the School of Public Health, University of California, Berkeley, Berkeley (B.D.F.), Children's Hospital Los Angeles (S.N.N., J.B., J.D.B.), the Department of Medicine, Division of Infectious Diseases (J.M., M.C., T.V., P.R.A., J.D.K.), and the Departments of Neurology (P.M.V.) and Pathology and Laboratory Medicine (S.C., R.M.H.), University of California, Los Angeles, Los Angeles, and the Departments of Pathology and Laboratory Medicine (C.D.G., F.M., N.A.O., C.R.P.) and Neurological Surgery (L.L.Z.) and the Department of Internal Medicine, Division of Infectious Diseases (S.H.C., C.R.P.), University of California, Davis, Davis - all in California; the Children's National Medical Center and George Washington University School of Medicine, Washington, DC (R.L.D.); St. Jude Children's Research Hospital, Memphis, TN (R.D., G.M., R.H.); and Children's Hospital Colorado, Aurora (K.M., S.R.D.).