Fig. 1.

Origin of blood donor samples and BTSs, identified by their headquarter locations (local language), participating in this project. The respective head quarter locations are given with their approximate geographical location and in their local languages. The area of each circle is correspondent to the number of samples investigated for each BTS (also see table 2). Approximately two-thirds of the analyzed blood donors (n = 24,058) were from the greater area of Zurich (blue circle), whereas the other third (n = 13,195) were from another 10 different blood transfusion services distributed throughout Switzerland (red circles), summing up to a total of 37,253 individual blood donor samples investigated in the course of this project. Topographically, Swiss Alps are shown in dark grey. Lugano and Sion are located south and Chur within the Swiss Alps.