1. Department of Pediatrics, University of Antwerp, Antwerp, Belgium;
2. Provincial Institute for Hygiene, Antwerp, Belgium;
3. VITO (Flemish Institute of Technological Research), Mol, Belgium;
4. Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium;
5. Center for Statistics, Hasselt University, Hasselt, Belgium;
6. Department of Microbiology, University of Antwerp, Antwerp, Belgium