1. Department of Infectious Disease Epidemiology, Helsinki, Finland; Department of Respiratory Medicine, Turku University Hospital, Preitilä, Finland
2. Department of Infectious Disease Epidemiology, National Public Health Institute, Helsinki, Finland
3. Department of Respiratory Medicine, Turku University Hospital, Preitilä, Finland
4. Department of Public Health, University of Helsinki, Helsinki, Finland
5. Department of Infectious Disease Epidemiology, Helsinki, Finland