Severe Chlamydia psittaci pneumonia: clinical characteristics and risk factors

Background: Psittacosis ranges from a mild illness to fulminant severe pneumonia with multi-organ failure. It's crucial to understand the clinical characteristics and identify risk factors for a better outcome. Methods: We conducted a retrospective analysis designed to identify risk factors for severe Chlamydia psittaci pneumonia (C. psittaci pneumonia) by comparing the clinical characteristics of patients with severe and less severe forms of the disease. Epidemiological, clinical, laboratory, computed tomography (CT) imaging, and outcome data were collected. Results: We enrolled 27 patients with C. psittaci pneumonia, with a median age of 63 (range 47-82) years, and 23 of whom (85.2%) had a history of avian exposure. Dyspnea was seen in 15 patients with severe C. psittaci pneumonia (100%), and four in 12 non-severe patients (33.3%) (P<0.01). Compared to nonsevere patients, those with severe C. psittaci pneumonia had significantly higher levels of procalcitonin, urea nitrogen, lactate dehydrogenase, creatine kinase (CK), B natriuretic peptide (BNP), myoglobin, IL-6, and IL-10, as well as lower lymphocyte and CD8+ T cell counts, and PaO2/FiO(2) ratio. Among patients with severe infection, CT showed that 46.7% had multi-lobar (more than two lobes) pneumonia, whereas its incidence was 0% in non-severe patients (P=0.01). Multivariate analysis revealed that the independent risk factors associated with severe C. psittaci pneumonia were abnormal CK (OR 15.2, 95% CI: 1.1-204.8, P=0.04) and BNP (OR 22.3, 95% CI: 1.8-281.9, P=0.02). Conclusions: A history of prior avian exposure in middle-aged patients should serve as a clue in the diagnosis of C. psittaci pneumonia, and patients with its severe form are more likely to develop dyspnea and progress into respiratory failure, with involvement of multiple lung lobes. Abnormal CK and BNP levels are risk factors associated with severe C. psittaci pneumonia.