Recent Chlamydia pneumoniae infection is highly associated with active ankylosing spondylitis in a Chinese cohort.

Objective: The aim of the present study was to investigate the presence of anti-Chlamydia pneumoniae (Cp) antibodies in patients with ankylosing spondylitis (AS) to determine whether there is an association with AS disease activity.Methods: Seventy-nine AS outpatients and 73 normal controls were enrolled in this case–control study. Serum anti-Cp immunoglobulins (CpIg) were detected by enzyme-linked immunosorbent assay (ELISA). Antibodies to Epstein–Barr virus (EBV), cytomegalovirus (CMV), and Chlamydia trachomatis (Ct) were also measured. Clinical and experimental data were collected, and the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) was determined. Patients with positive Cp IgM or Cp IgA were considered to have had a recent Cp infection.Results: Cp IgG was detected in the majority of AS patients and also controls (88.8% vs. 91.8%, respectively). The seroprevalence of Cp IgA and Cp IgM was significantly higher in AS patients than in the controls (51.9% vs. 31.5%, p = 0.010 for Cp IgA; 79...