Background Recent evidence indicates that subclinical infection by Chlamydophila psittaci occurs in a significant percentage of patients with chronic inflammatory polyarthritis, including psoriatic arthritis. Objective To assess the prevalence of Chlamydiae infection in a large cohort of well-characterized patients with psoriasis. Methods The presence of a subclinical C. psittaci infection was investigated in 64 patients with psoriasis, including 12 patients with psoriatic arthritis. Two hundred and twenty-five healthy controls were also investigated. The presence of infection was assessed in peripheral blood mononuclear cells using several polymerase chain reaction protocols, targeting different regions of the bacterial genome. The DNA of other species (Chlamydophila pneumoniae and Chlamydia trachomatis) was also investigated. Results Chlamydophila psittaci infection was observed in a significantly higher percentage of patients with psoriasis (11/64, 17%) compared with healthy controls (1/225, 0·4%) (odds ratio 46·49, 95% confidence interval 5·87-368·03; P <0·0001). No differences in age, sex or disease duration were noticed between positive and negative patients, but the majority of the positive patients were on immunomodulatory treatments. Conclusion Chlamydophila psittaci may be an infectious trigger possibly involved in the pathogenesis of psoriasis.
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