Diagnosis of C. pneumoniae pneumonia is still debated in the current literature. According to Grayston et al. and Saikku et al. [19, 20] , who first described this Chlamydia species, almost everybody is infected and reinfected with C. pneumoniae throughout his or her life. Unspecific symptoms of C. pneumoniae infections make the diagnosis even more difficult, with a possible underestimation of its frequency. Undetected infections may lead to chronic disease with serious consequences, such as atherosclerotic cardiovascular disease [21] or asthma. Its incidence in CAP ranges from 3% to 22%, varying according to the diagnostic method used [22] . The most frequent routinely used diagnostic techniques are serological, including complement fixation test, immunofluorescence assay, microimmunofluorescence (MIF) and genus-and species-specific enzyme-linked immunosorbent assay (ELISA) systems. No currently available serologic tests of a single serum specimen will provide conclusive evidence of a current infection with C. pneumoniae.