1. Department of Oral Biology, Dental Faculty, University of Oslo, Oslo, Norway
2. Laboratoire Mixte Médecine-Odontologie, Ecologie Microbienne et Résistance aux Antibiotiques, Hopital L'Archet 2, Centre Hospitalier Universitaire de Nice, Nice, France
3. Department of Airborne Infections, Norwegian Institute of Public Health, Oslo, Norway