Evaluation of serological tests for diagnosis of Chlamydophila pneumoniae pneumonia in patients with nursing and healthcare-associated pneumonia

Nursing and healthcare-associated pneumonia (NHCAP) is a new category that is distinct from community-acquired pneumonia that has been documented in the 2011 Japanese Respiratory Society (JRS) guidelines. We aimed to evaluate an ELNAS Plate test for detecting anti-Chlamydophila pneumoniae-specific immunoglobulin M (IgM) antibodies in patients with NHCAP, by comparing the results of the ELNAS test with those of the Hitazyme enzyme-linked immunosorbent assay (Hitazyme-ELISA) and those of immunoblotting and microimmunofluorescence (MIF) tests. During the study period, we enrolled 739 patients with pneumonia in a university hospital and 812 patients with pneumonia in a community hospital; of these, 250 (34 %) and 349 (43 %), respectively, were classified as having NHCAP. C. pneumoniae pneumonia was detected in five cases by the MIF test and ELNAS test. All five cases demonstrated significant IgG antibody seroconversion, while one case was IgM-positive. Sixty-seven of the total of 599 patients (11 %) were C. pneumoniae IgM-positive on the Hitazyme-ELISA. One of the IgM-positive cases was confirmed by other methods and was shown to be a true positive. In the remaining cases, however, three other tests-the ELNAS test, the MIF test, and immunoblotting analysis-did not reveal any positive cases. The ELNAS, Hitazyme-ELISA, and MIF tests did not detect any significant increases in IgG or IgA antibody titers between paired sera. The results of the newly available ELNAS test for detecting anti-C. pneumoniae-specific IgM antibody correlated well with the results of the other established serological tests. To increase the diagnostic rate in patients with NHCAP, physicians should measure IgG antibody rather than IgM antibody using paired sera.