ANTIBODIES OF CHLAMYDIA SPECIES IN PATIENTS ATTENDING A GENITOURINARY CLINIC AND THE IMPACT OF ANTIBODIES TO C-PNEUMONIAE AND C-PSITTACI ON THE SENSITIVITY AND THE SPECIFICITY OF C-TRACHOMATIS SEROLOGY TESTS

In a retrospective study, the prevalence of antibodies to Chlamydia trachomatis serovars D to K, C. pneumoniae, and C. psittaci in cases attending a genitourinary, clinic was examined. Blood samples were collected from 7,002 cases attending the clinic in Doncaster, England between May 1983 and May 1990. Sera from these samples were tested by a modified microimmunofluorescence test using panels of microdots of egg-grown, purified elementary bodies representing a pool of C. trachomatis D to K, a single C. pneumoniae agent, a single C. psittaci agent, and a negative control. Serum specimens were tested for the presence of IgG and IgM at starting dilutions of 1/16 and 1/8, respectively. Chlamydial IgG at a level of 1/16 or higher and IgM at a level of 1/8 or higher was present in 66.6% and 2.6% of samples, respectively. Species-specific or cross-reactive IgG against C. trachomatis D to K, C. pneumoniae, and C. psittaci was present in 32.6%, 25.1%, and 0.1% of the samples, respectively. In 8.7% of samples, the level of IgG was similar against two or all three species (group-specific). IgM against C. trachomatis D to K, C. pneumoniae, or C. psittaci was present in 2.5%, 0.03%, and 0.04% of the samples, respectively. The results of the study show that antibodies to C. pneumoniae and C. psittaci account for up to half of all chlamydia IgG positive cases attending genitourinary clinics. We therefore recommend that a serologic test that can differentiate antibodies to C. trachomatis from those to C. pneumoniae and C. psittaci, such as the modified microimmunofluorescence test, should be used for screening and for presumptive serodiagnosis of genital infections.