Abstract: Disclosed is a method for determining a possible bacterial infection in a patient exhibiting symptoms selected from specific internal symptoms of disease, and/or diffuse and general manifestations of disease, and/or is a blood donor. The method includes: i) determining a) the level of a Rickettsia analyte in a sample 1 from a patient exhibiting symptoms, possibly combined with b) the level of a Borrelia analyte in a sample 2 from the same patient; ii) considering that the symptoms exhibited by the patient involve a) rickettsiosis if the level of the Rickettsia analyte in sample 1 is elevated, and b) borrelios if the level of the Borrelia analyte in sample 2 is elevated. For blood donors step, (ii) means that whole blood and blood fractions are considered to be infected with Rickettsia and/or Borrelia, respectively, when these levels are elevated. Also disclosed is a corresponding kit.