1. CIBER Epidemiology and Public Health CIBERESP Institute Carlos III Madrid Spain
2. Department of Medicine University of Barcelona Barcelona Spain
3. Division of Viral Diseases, Centers for Disease Control and Prevention National Center for Immunization and Respiratory Diseases Atlanta Georgia USA
4. Public Health Agency of Catalonia Barcelona Spain
5. Virology Unit, Centre de Diagnòstic Biomèdic Hospital Clínic Barcelona Spain