Chlamydial DNA is absent from the joints of patients with sexually acquired reactive arthritis.

The polymerase chain reaction was used to detect the presence of a plasmid essential for the growth of Chlamydia trachomatis. As few as 10 copies of the plasmid in the initial reaction mix were detectable using this technique. In contrast, chlamydial DNA was not detectable in the knee joints of nine patients with definite sexually acquired reactive arthritis (SARA) or nine patients with suspected SARA. Five patients with an undifferentiated seronegative lower limb oligoarthropathy, one with Crohn's disease and another with post-enteric reactive arthritis had evidence of intra-articular chlamydial antigens as judged by fluorescein-labelled monoclonal antibody staining of joint material but, again, no chlamydia plasmid DNA was detected. The nature of the immunofluorescent staining seen in some of these samples remains to be elucidated. It could be due to the presence of chlamydial outer membrane protein or lipopolysaccharide antigens in the joints, either free or in immune complexes, or it may be artefactual. Our results indicate that viable C. trachomatis is not present in the joints of the patients in this study even in the presence of chlamydial antigen detected by fluorescence antibody testing.