1. The Heart Center, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark (H.B., J.S.B., D.E.T., M.M.P., C.R.V., U.C.W., A.R.)
2. Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark (C.V., T.T., H.U.)
3. Herlev & Gentofte Hospital, Copenhagen University Hospital, Herlev, Denmark (J.B.N., P.B.N., K.F., R.H., J.H.K., K.I.)
4. Nordsjaellands Hospital, Hillerød, and Aalborg University Hospital, Aalborg, Denmark (M.P.A., C.T.)
5. Centre for Diagnostics, Technical University of Denmark, Kongens Lyngby, Denmark (N.B.G.)
6. National Influenza Center, Statens Serum Institut, Copenhagen, Denmark (R.T.)
7. Technical University of Denmark, Kongens Lyngby, Denmark (K.S.)
8. Center of Research & Disruption of Infectious Diseases, Amager and Hvidovre Hospital, Copenhagen University Hospital, Hvidovre, Denmark (T.B.).