Analysis of Risk Factors for Severe Pneumonia Progression in Chlamydia psittaci Infections: A Retrospective Study.

Introduction: Psittacosis pneumonia, caused by Chlamydia psittaci, is a zoonotic infection with a severe-case mortality rate of 15-20%. This study aimed to identify risk factors for severe pneumonia and evaluate the discriminative performance of corresponding predictive models.

Methods: In this retrospective study, 51 patients with metagenomic next-generation sequencing (mNGS)-confirmed psittacosis pneumonia were classified into severe (n=20) and non-severe (n=31) groups. Demographic characteristics, clinical manifestations, laboratory parameters, and imaging features were collected. Variables were analyzed using univariate screening, variance inflation factor (VIF)-based multicollinearity control, least absolute shrinkage and selection operator (LASSO) regression, and Firth-penalized logistic regression. Receiver operating characteristic (ROC) analysis evaluated predictive performance.

Results: Patients with severe pneumonia were significantly older (p = 0.043) and showed a higher prevalence of underlying diseases (p = 0.025) and cardiovascular diseases (CVD, p = 0.028). They also exhibited persistent lymphocytopenia, progressive decreases in hemoglobin (Hb) levels, and a higher rate of bilateral lung involvement. LASSO regression identified four key predictors: history of CVD, first lymphocyte count (LYM), second Hb measurement, and lactate dehydrogenase (LDH) level. Firth-penalized logistic regression confirmed that a history of CVD (OR = 4.874, 95% CI: 1.270-22.763) and a decreased second Hb measurement (OR = 0.415, 95% CI: 0.169-0.844) were independent risk factors for severe pneumonia. ROC analysis demonstrated that the combination of CVD history and the second Hb measurement achieved a specificity of 90.32%, while the combination of CVD history and LDH exhibited a sensitivity of 90%. The final multivariable model showed good discriminatory performance, with an area under the curve (AUC) of 0.885, sensitivity of 75%, and specificity of 93.50%.

Conclusion: CVD history and progressive Hb decrease are independent risk factors for severe psittacosis pneumonia. Dynamic monitoring of LYM, Hb, LDH, and CVD history facilitates early risk stratification. The multivariate model demonstrates high predictive accuracy and clinical utility.