1. Department of Public Health, Work, Environment and Health, Danish Ramazzini Centre, Aarhus University , DK-8000 Aarhus C , Denmark
2. Department of Occupational Medicine, Danish Ramazzini Centre, Aarhus University Hospital , DK-8200 Aarhus N , Denmark
3. Department of Occupational Medicine, Danish Ramazzini Centre, Goedstrup Hospital , DK-7400 Herning , Denmark
4. Department of Occupational and Environmental Medicine, Bispebjerg and Frederiksberg Hospital, University of Copenhagen , DK-2400 Copenhagen , Denmark
5. Department of Clinical Microbiology, Aarhus University Hospital , DK-8200 Aarhus N , Denmark
6. National Research Center for the Working Environment , DK-2100 Copenhagen , Denmark