1. Department of Clinical Microbiology, Division of Infectious Diseases, Umeå University, S-901 85 Umeå, Sweden
2. Department of Clinical Microbiology, Division of Virology, Umeå University, S-901 85 Umeå, Sweden
3. Center for Infectious Medicine, Department of Medicine, Karolinska Institutet, Karolinska University Hospital Huddinge, S-141 86 Stockholm, Sweden