1. From the Department of Epidemiology and Public Health, University College London, London, UK (N.N.C., H.M.C.); the Department of Virology, Royal Free and University College School of Medicine, Royal Free Campus, London, UK (D.A., V.E.); the Department of Medicine, Royal Free and University College Medical School, London, UK (C.G.-C., D.J.B., P.V.); and the Department of Clinical Microbiology, University College London Hospitals, London, UK (G.L.R.).