1. Division of Clinical Virology, Department of Immunology, Microbiology, Pathology, and Infectious Diseases, Karolinska Institutet, Huddinge University Hospital, S-141 86 Stockholm, Sweden
2. Division of Clinical Virology, Department of Immunology, Microbiology, Pathology, and Infectious Diseases, Karolinska Institutet, Huddinge University Hospital, S-141 86 Stockholm, Sweden and Division of Infectious Diseases, Department of Medicine, Karolinska Institutet, Huddinge University Hospital, S-141 86 Stockholm, Sweden
3. Division of Infectious Diseases, Department of Medicine, Karolinska Institutet, Huddinge University Hospital, S-141 86 Stockholm, Sweden
4. Swedish Institute for Infectious Disease Control/Karolinska Institutet, 17182 Solna, Sweden
5. Department of Microbiology, University of Washington, Seattle, Washington 98195