Usefulness of enzyme linked immunosorbent assays species specific in the detection of Chlamydia trachomatis and Chlamydophila pneumoniae IgG antibodies in patients with genital infections or respiratory tract infections

Chlamydia trachomatis (Ct) and Chlamydophila pneumoniae (Cpn) are obligate intracellular bacteria causing genital tract infections (GTI) and respiratory tract infections (RTI), respectively. Antigenic cross-reactivity between the two species may complicate serologic diagnosis. In this study, we compared the performance of two ELISA tests in relation to microimmunofluorescence (MIF) for the detection of Ct and Cpn IgG antibodies. We also explored the degree of cross-reactivity by ELISA and MIF. Among 278 positive sera for Cpn and/or Ct IgG antibodies in the MIF, 153 were from patients with GTI and 125 were from patients with RTI. These sera were tested by our in house MIF test and by two commercial ELISA: SeroCP and SeroCT for the detection of anti-Cpn IgG antibodies and anti-Ct IgG antibodies, respectively. In sera from patients with RTI, correlation between MIF and SeroCP was 92%. The specificity of this test was 38.5%. In fact, among the 140 sera from patients with GTI and that cross-reacted in MIF, only six were confirmed by the two ELISA tests as having IgG antibodies to Ct. The correlation between MIF and SeroCT was 80%. The specificity of this test was 100%. Indeed, among the 65 sera from patients with RTI with cross-reactions in MIF, 30 sera showed a negative SeroCT test. SeroCT was highly specific and could diminish considerably the extent of cross-reactions. Whilst, SeroCP test was not specific enough to distinguish between the presence of IgG antibodies and Cpn or Ct.