Screening for antibody to Chlamydia pneumoniae by the complement fixation test

We performed a retrospective survey for antibody to Chlamydia pneumoniae, by the microimmunofluorescence (MIF) test, on 120 sera that were previously determined to be positive for antibody to ornithosis antigen by the complement fixation (CF) test. The panel of sera comprised 40 paired acute and convalescent sera, and 40 single samples, from 80 patients. Of these patients, 60% were considered to be serologically positive for C. pneumoniae, based on the antibody titers of IgG, IgM, or both. There was no association between the CF titer to ornithosis antigen and the respective IgG or IgM MIF antibody titers. We propose that, in those laboratories routinely using the CF test, sera found to be positive for ornithosis antigen should be further tested by the MIF in order to clarify, both from an epidemiologic and clinical perspective, whether these patients are also serologically positive for C. pneumoniae.