Since the risk of acquiring Lyme borreliosis may be increasing as a consequence of a complex interplay between climate change, anthropogenic factors and number of infected ticks, the primary aim of our investigation was to obtain current estimates of IgG and IgM seropositivity for B. burgdorferi s.l. in the Rhineland Study population in Bonn, Germany, and to compare them to previous estimates from other studies with data from NRW, the federal state in which Bonn is situated. Here, CD40LG is linked to Lyme disease.