Chlamydophila pneumoniae diagnostics: importance of methodology in relation to timing of sampling

The diagnostic impact of PCR-based detection was compared to single-serum IgM antibody measurement and IgG antibody seroconversion during an outbreak of Chlamydophila pneumoniae in a military community. Nasopharyngeal swabs for PCR-based detection, and serum, were obtained from 127 conscripts during the outbreak. Serum, drawn many months before the outbreak, provided the baseline antibody status. C. pneumoniae IgM and IgG antibodies were assayed using microimmunofluorescence (MIF), enzyme immunoassay (EIA) and recombinant ELISA (rELISA). Two reference standard tests were applied: (i) C. pneumoniae PCR; and (ii) assay of C. pneumoniae IgM antibodies, defined as positive if >or=2 IgM antibody assays (i.e. rELISA with MIF and/or EIA) were positive. In 33 subjects, of whom two tested negative according to IgM antibody assays and IgG seroconversion, C. pneumoniae DNA was detected by PCR. The sensitivities were 79%, 85%, 88% and 68%, respectively, and the specificities were 86%, 84%, 78% and 93%, respectively, for MIF IgM, EIA IgM, rELISA IgM and PCR. In two subjects, acute infection was diagnosed on the basis of IgG antibody seroconversion alone. The sensitivity of PCR detection was lower than that of any IgM antibody assay. This may be explained by the late sampling, or clearance of the organism following antibiotic treatment. The results of assay evaluation studies are affected not only by the choice of reference standard tests, but also by the timing of sampling for the different test principles used. On the basis of these findings, a combination of nasopharyngeal swabbing for PCR detection and specific single-serum IgM measurement is recommended in cases of acute respiratory C. pneumoniae infection.