Admission clinical features associated with disease severity in psittacosis pneumonia: A retrospective study

Psittacosis pneumonia caused by Chlamydia psittaci is often difficult to diagnose. Objective severity risk stratification at hospital admission is crucial for clinical management but remains challenging. This retrospective study aimed to evaluate admission baseline clinical characteristics for severity risk stratification in patients with psittacosis pneumonia.

We analyzed 60 patients diagnosed with psittacosis pneumonia, comprising 31 severe and 29 non-severe cases. All clinical and laboratory data were obtained from the initial evaluation within 24 h of admission. Firth penalized logistic regression was employed to identify potential indicators associated with disease severity.

Of 60 patients with confirmed psittacosis pneumonia, 31 (52%) were classified as severe and had a higher frequency of respiratory failure, longer hospitalization, and more complications. Severe cases exhibited higher levels of CRP, PCT, d-dimer, LDH, AST, and BUN, lower albumin and lymphocyte counts, and more frequent bilateral lung lesions. Higher Strictly Mapped Read Number (SMRN) of C. psittaci was observed in severe cases, whereas monoinfection predominated in non-severe cases. Firth penalized logistic regression identified d-dimer, monocyte count, and LDH as key variables for admission risk stratification. The model showed good discriminative performance for admission risk stratification (AUC=0.888).

Baseline d-dimer, monocyte count, and lactate dehydrogenase (LDH) appear to reflect distinct pathophysiological processes, including coagulation activation, inflammatory response, and systemic tissue injury. Their integration offers a potential framework for objective severity risk stratification at hospital admission. Such assessments may assist in clinical triage and the optimization of resource allocation for patients with psittacosis pneumonia.