In a pilot study, Hedlund et al. (Hedlund and Hansson, 2000) suggested that PCT might aid the physician to differentiate typical bacterial community-acquired pneumoniae (CAP) etiology from atypical etiology: 8/9 patients with pneumonia caused by atypical agents had PCT levels <0.5 ng/ml compared with 6/27 patients with pneumonia caused by classic bacterial pathogens, mainly Streptococcus pneumoniae (p = 0.03). Here, CALCA is linked to pneumonia.