1. Microbiology and Tumor Biology Center, Karolinska Institutet, S 17177 Stockholm, Sweden and Division of Microbiology, Department of Molecular Biology, University of Siena, 53100 Siena, Italy
2. Gay Men's Health Clinic, Söder Hospital, 11883 Stockholm, Sweden
3. Division of Clinical Virology, Karolinska Institutet, Huddinge University Hospital, 14186 Stockholm, Sweden
4. Division of Clinical Virology, Karolinska Institutet, Huddinge University Hospital, 14186 Stockholm, Sweden.
5. Division of Microbiology, Department of Molecular Biology, University of Siena, 53100 Siena, Italy and Laboratory of Microbiology and Virology, General Hospital, 53100 Siena, Italy
6. Microbiology and Tumor Biology Center, Karolinska Institutet, S 17177 Stockholm, Sweden