1. Virology, University of Helsinki and Helsinki University Hospital, Helsinki, Finland
2. Infectious Disease Control Unit, Department of Infectious Diseases, National Institute for Health and Welfare, Helsinki, Finland
3. Department of Veterinary Biosciences, Faculty of Veterinary Medicine, University of Helsinki, Helsinki, Finland
4. Department of Medical Microbiology and Immunology, University of Turku, Turku, Finland
5. Health Monitoring Unit, Department of Health, National Institute for Health and Welfare, Helsinki, Finland
6. Suonenjoki Unit, Natural Resources Institute, Suonenjoki, Finland
7. Vantaa Unit, Natural Resources Institute, Vantaa, Finland