1. Division of Infectious Disease Control, Norwegian Institute of Public Health, Oslo, Norway.
2. Department of Microbiology and Infection Control, University Hospital of North Norway, Tromsø, Norway.
3. Department of Microbiology and Virology, Institute of Medical Biology, Faculty of Medicine, University of Tromsø, Tromsø, Norway.
4. Department of Oral Biology, University of Oslo, Oslo, Norway.