1. Department of Paediatrics; Ostfold Hospital Trust; Grålum Norway
2. Infection Control and Environmental Health; Norwegian Institute of Public Health; Oslo Norway
3. Institute of Laboratory Medicine; Children's and Women's Health; Norwegian University of Science and Technology; Trondheim Norway
4. Department of Paediatrics; St Olavs University Hospital; Trondheim Norway
5. Department of Paediatrics; Stavanger University Hospital; Stavanger Norway
6. Department of Paediatrics; Oslo University Hospital; Ullevaal Norway
7. Child Health; Norwegian Institute of Public Health; Oslo Norway