Retrospective Analysis of Clinical Characteristics and Prognostic Factors in Hospitalized Pneumonia Patients from April 2023 to April 2026. Background: Pneumonia remains the leading cause of death from infectious diseases in adults worldwide, with an increasingly severe disease burden exacerbated by population aging and the frequent emergence of drug-resistant bacteria; in China, severe pneumonia accounts for a striking 13.58% to 20.05% of hospitalized cases. In recent years, shifts in the pathogen spectrum (e.g., COVID-19, influenza A) and patient demographic characteristics have posed new challenges for clinical management. However, existing studies mostly focus on single pathogens or specific populations (e.g., ICU patients), lacking systematic analyses of the full-disease course characteristics of general hospitalized pneumonia patients. Furthermore, in the post-pandemic era, the clinical phenotypes, treatment responses, and prognostic factors of pneumonia may have evolved, necessitating evidence-based support from real-world data. This study aims to conduct a retrospective analysis to clarify the epidemiological characteristics, etiological distribution, and prognostic factors influencing current hospitalized pneumonia patients, thereby providing a basis for optimizing diagnosis and treatment strategies.

Inclusion Criteria:

1. Age ≥ 18 years old;

2. Meet the diagnostic criteria for pneumonia (acute onset + new infiltrates on imaging);

3. Have a positive result from pathogen testing;

4. Time from onset to admission ≤ 72 hours (to ensure being in the acute phase of the disease);

5. Sign a written informed consent form.

   Inclusion criteria for the severe group:

   A diagnosis of "severe pneumonia" can be made if one of the main criteria or ≥ 3 of the secondary criteria are met.

   Main criteria:

   ① Tracheal intubation requiring mechanical ventilation

   ② Need for vasoactive drugs after active fluid resuscitation for septic shock

   Secondary criteria:

   • Respiratory rate ≥ 30 breaths/min

     • PaO₂/FiO₂ ≤ 250 mm Hg

       • Multiple lobe infiltrates

         • Confusion and/or disorientation ⑤ Blood urea nitrogen ≥ 20 mg/dL

           ⑥ Leukopenia (WBC < 4×10⁹/L)

           • Thrombocytopenia (PLT < 100×10⁹/L)

             • Decreased body temperature (central body temperature < 36 ℃) ⑨ Hypotension requiring fluid resuscitation

   Exclusion Criteria:

   • 1) Patients with severely lacking medical records;

2) Those whose main manifestations are other non-infectious diseases (such as pulmonary edema, lung cancer, pulmonary embolism, etc.); 3) Those whose main diagnosis is active pulmonary tuberculosis, non-infectious interstitial lung disease, etc.; 4) Patients considered not applicable by the researchers.

From April 2023 to April 2026, all adult patients who were hospitalized due to pneumonia and met the diagnostic criteria

Due to concerns over patient privacy and confidentiality issues, the individual patient data (IPD) cannot be shared.