Evaluation of serological tests detecting Chlamydophila pneumoniae-specific immunoglobulin M antibody

To evaluate a newly developed enzyme-linked immunosorbent assay (ELISA) (Hitazyme C. pneumoniae) detecting Chlamydophila pneumoniae-specific immunoglobulin M (IgM) antibody, we compared the assay with culturing, immunoblotting and the microimmunofluorescence (MIF) test.

Two hundred five patients with stable chronic lung diseases without acute respiratory tract infections (ARTIs) and 116 healthy volunteers without ARTIs were enrolled in this study. Nasopharyngeal swab specimens and sera were obtained from all subjects for isolation and serological testing of C. pneumoniae.

C. pneumoniae IgM-positive results were observed in 16.5% of patients with stable chronic lung diseases and in 8.6% of asymptomatic healthy subjects. However, there were no positive cases with cell culture, immunoblot or MIF test. In addition, no cases with a significant increase in IgA or IgG antibody titer for the ELISA kit and MIF test between paired sera were observed in the followed-up groups. IgM-positive cases were more frequent among patients with chronic obstructive pulmonary disease (p=0.1566), collagen disease-associated interstitial lung disease (p<0.0001) and cryptogenic organizing pneumonia (p=0.0199) than among the healthy subjects.

Our results indicate that IgM-positive results with the ELISA kit do not always reflect acute C. pneumoniae infections. Further studies are needed, to determine an appropriate cut-off level and the possible causes of the false-positive results in the ELISA kit, such as other underlying conditions.