1. Division of Clinical Virology, Department of Laboratory Medicine, Karolinska Institute, Huddinge University Hospital, S-141 86 Huddinge/Stockholm, Sweden and Department of Virology, Swedish Institute for Infectious Disease Control, Solna, Sweden.
2. Department of Medicine, Unit of Infectious Diseases, Karolinska Institute, Karolinska Hospital, Stockholm, Sweden
3. Department of Infectious Diseases, Huddinge University Hospital, S-141 86 Huddinge/Stockholm, Sweden
4. Department of Infectious Diseases, Sahlgrenska University Hospital, Göteborg, Sweden
5. Division of Clinical Virology, Department of Laboratory Medicine, Karolinska Institute, Huddinge University Hospital, S-141 86 Huddinge/Stockholm, Sweden
6. Department of Emergency and Acute Services Unit of Infectious Diseases, Helsingborg Hospital, Helsingborg, Sweden. 6Present address: Department of Virology, Swedish Institute for Infectious Disease Control, Solna, Sweden