1. Department of Environmental Health, National Institute for Health and Welfare, Kuopio, Finland;
2. Pediatric Research Center, Tampere University and University Hospital, University of Tampere, Tampere, Finland;
3. Institute for Laboratory Medicine and Pathobiochemistry, Molecular Diagnostics, Philipps-University Marburg, Marburg, Germany;
4. Department of Pediatrics, Kuopio University Hospital, Kuopio, Finland;
5. Institute of Epidemiology and Medical Biometry, Ulm University, Ulm, Germany; and
6. Department of Public Health, University of Helsinki, Helsinki, Finland