1. Department of International Health, Immunology and Microbiology, Faculty of Health Sciences, University of Copenhagen, 1353 Copenhagen K, Denmark
2. Department of Occupational and Environmental Medicine, Odense University Hospital, 5000 Odense C, Denmark
3. Department of Biostatistics, Institute of Public Health, University of Copenhagen, 2200 Copenhagen N, Denmark
4. Department of Veterinary Disease Biology, Faculty of Life Sciences, University of Copenhagen, 1870 Frederiksberg C, Denmark