1. Microbiology and Tumor Biology Center, Karolinska Institutet, SE-171 77 Stockholm, Sweden.
2. Department of Clinical Virology, The Swedish Institute of Infectious Disease Control, SE-172 82 Solna, Sweden.
3. Unit of Neonatal Health, Department of Women's and Children's Health, Karolinska Institutet, SE-171 77 Stockholm, Sweden.
4. Division of Obstetrics and Gynecology, Department of Clinical Science, Karolinska University Hospital Huddinge, Karolinska Institutet, SE-171 77 Stockholm, Sweden.
5. Division of Pediatrics, Department of Clinical Science, Karolinska University Hospital Huddinge, Karolinska Institutet, SE-171 77 Stockholm, Sweden.
6. Department of Medical Microbiology, Dermatology, and Infection, Lund University Hospital, Lund, Sweden.
7. Theoretical Biology and Biophysics Group, Los Alamos National Laboratory, Los Alamos, New Mexico 87545.
8. Department of Laboratory Medicine, Division of Clinical Virology, Karolinska University Hospital Huddinge, Karolinska Institutet, SE-171 77 Stockholm, Sweden.