This is possibly related to the intrinsically increased PCT caused by the primary disease per se since HFRS patients without bacterial infection had a higher serum PCT level [0.94 ng/ml (range 0.05–25 ng/ml)] than the normal reference value (<0.5 ng/ml) and this may compromise the performance of PCT in identifying bacterial infections in this specific disease condition. Here, CALCA is linked to bacterial infectious disease.