Published on in Vol 6, No 4 (2018): Oct-Dec
                                    Preprints (earlier versions) of this paper are
                                    available at
                                    https://preprints.jmir.org/preprint/11428, first published
                                    .
                                

1 Department of Public Health and Primary Care, KU Leuven, Leuven, Belgium
2 Sciensano, Brussels, Belgium
