Overview of the participating study centers and swabbing methods applied. Abbreviations used: N (staff) = nasal swabs collected by certified personnel in the study center; N (self) = nasal swabs self-collected by the participants at home; OP = oropharyngeal swabs collected by certified personnel in the study center. The map was taken from: http://commons.wikimedia.org/wiki/Image:Karte_Bundesrepublik_Deutschland.svg and edited by the author (MKA). Name of the creator of the source map is David Liuzzo. Link to the license: https://commons.wikimedia.org/wiki/Commons:Reusing_content_outside_Wikimedia. The map was published under the CC Creative Commons Attribution-ShareAlike 2.5 Generic (CC BY-SA 2.5) license, which allows (https://creativecommons.org/licenses/by-sa/2.5/deed.en): • Share - copy and redistribute the material in any medium or format • Adapt - remix, transform, and build upon the material for any purpose, even commercially. • The licensor cannot revoke these freedoms as long as you follow the license terms.