Adaptive RCT of Corticosteroids for Severe Chlamydia Psittaci Pneumonia in Adults

Inclusion Criteria: * Age ≥ 18 years. * Admission to the Intensive Care Unit (ICU). * Meeting the diagnostic criteria for community-acquired pneumonia (CAP). * Meeting at least one of the major diagnostic criteria for severe pneumonia: (i) Requirement for endotracheal intubation and mechanical ventilation; (ii) Septic shock requiring vasopressor therapy after adequate fluid resuscitation. -Or simultaneously fulfilling three of the minor criteria: (i) Respiratory rate ≥ 30 breaths/min; (ii) PaO₂/FiO₂ ≤ 250 mmHg; (iii) Multilobar infiltrates; (iv) Altered mental status and/or disorientation; (v) Blood urea nitrogen ≥ 20 mg/dL (7.12 mmol/L); (vi) Leukopenia (white blood cell count \< 4 × 10⁹/L); (vii) Thrombocytopenia (platelet count \< 100 × 10⁹/L); (viii) Hypothermia (core temperature \< 36 °C); (ix) Hypotension (systolic blood pressure \< 90 mmHg) requiring aggressive fluid resuscitation. * Confirmed Chlamydia psittaci etiology (psittacosis): at least one positive nucleic acid test (PCR/RT-PCR) or next-generation sequencing (NGS) result for Chlamydia psittaci in respiratory specimens (respiratory secretions, throat swabs, or bronchoalveolar lavage fluid). * Severe community-acquired pneumonia (SCAP) patients admitted to the emergency department/ward/ICU due to respiratory failure within \< 72 hours. * Signed informed consent. Exclusion Criteria: * Patients receiving vasopressor therapy for septic shock at the time of enrollment. * Terminally ill patients (expected survival \<30 days, e.g., advanced malignancy). * Clinical history suggesting overt aspiration. * Documented active gastrointestinal bleeding. * Presence of cystic fibrosis, obstructive pneumonia, active influenza, pulmonary tuberculosis, or fungal infection. * Active viral hepatitis or active herpesvirus infection. * Bone marrow suppression or HIV infection. * Refusal of mechanical ventilation and endotracheal intubation. * Uncontrolled hyperglycemia (diabetic ketoacidosis with blood ketones \>3 mmol/L, or hyperosmolar hyperglycemic state with blood glucose \>33.3 mmol/L and elevated osmolality). * Known allergy to corticosteroids. * Patients requiring anti-inflammatory corticosteroids or replacement hydrocortisone for any reason, or those already receiving prednisone \>15 mg/day (or equivalent dose of another corticosteroid). * Pregnant or breastfeeding women.