Author Contributions: Dr Janssens had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. Study concept and design: Janssens, Pavel, Antoniou, Diepgen, de Gruijl, and Rhodes. Acquisition of data: Janssens, Ling, Winhoven, Anastasopoulou, Stratigos, and Rhodes. Analysis and interpretation of data: Janssens, de Gruijl, and Rhodes. Drafting of the manuscript: Janssens, Winhoven, Anastasopolou, Diepgen, and Rhodes. Critical revision of the manuscript for important intellectual content: Janssens, Pavel, Ling, Stratigos, Antoniou, de Gruijl, and Rhodes. Statistical analysis: Janssens. Obtained funding: de Gruijl. Administrative, technical, and material support: Janssens, Antoniou, Anastasopoulou, de Gruijl, and Rhodes. Study supervision: Pavel, Stratigos, Diepgen, de Gruijl, and Rhodes.