Evaluation of a direct fluorescent antibody assay for detection of Chlamydia pneumoniae.

We examined the utility of the direct immunofluorescent antibody test kit, IMAGEN (DAKO Diagnostic Co., Ltd.). The stainability of inclusions and purified elementary bodies (EBs) of all the Chlamydia pneumoniae strains used in this study was highly specific. Immunoelectron microscopy and light microscopy of stained EBs revealed the target antigen of IMAGEN to be located on the surface of the EB outer membrane. In a clinical study, we tested oropharyngeal swab specimens obtained from 41 patients (45 specimens). The results were compared with those obtained by isolation in cell culture, the indirect immunofluorescent antibody (IFA) assay and serum antibody titration. C. pneumoniae was isolated from six specimens (13.3%), and the organisms were detected in 11 specimens (24.4%) with IMAGEN and nine specimens (20%) with IFA. A diagnosis of C. pneumoniae infection was made in six patients (13.3%) by the serological examination. Six specimens positive in isolation were positive in the IMAGEN but there were three cases which seemed to be false-positive by the IMAGEN. We conclude that the use of IMAGEN is an easy, rapid and sensitive method for detecting C. pneumoniae when there is a large amount of chlamydial antigen in the clinical specimen and when identification of the chlamydial species forming inclusions in cell cultures is required.