Expanded Diagnostic Strategy in Older Adults Hospitalized With Community-Acquired Acute Respiratory Infection

This study will evaluate whether an expanded diagnostic strategy can reduce antibiotic use in patients aged 65 years or older who are hospitalized with community-acquired acute respiratory infection, without negatively affecting clinical outcomes. The expanded diagnostic strategy combines multiplex respiratory polymerase chain reaction (PCR), serial procalcitonin measurements, and bedside lung ultrasound. The results of these tests will be integrated to support decisions about antibiotic treatment. The study will compare the expanded diagnostic strategy with conventional diagnostic management. The main outcome will be the total duration of antibiotic therapy. The study will also assess the use of high-impact antibiotics, microbiological diagnosis, hospital and intensive care unit stay, complications, mortality, recurrence of infection, hospital readmissions, detection of multidrug-resistant microorganisms, and antibiotic-related adverse events.

Inclusion Criteria: * Age ≥ 65 years. * Hospital admission to the Internal Medicine or Infectious Diseases ward for a community-acquired acute respiratory infection. * Acute respiratory infection defined by the presence of at least two of the following criteria, with at least one being a clinical criterion: * Clinical criteria: new-onset cough or worsening of pre-existing cough; purulent sputum production or changes in usual sputum characteristics; new-onset dyspnea or worsening of pre-existing dyspnea; pleuritic chest pain; abnormal respiratory sounds (crackles, rhonchi, or wheezing); fever (temperature ≥ 38°C) or hypothermia (temperature \< 36°C). * Laboratory criteria: leukocytosis (white blood cell count \> 11,000/µL or neutrophil count \> 8,200/µL) or C-reactive protein ≥ 20 mg/L. * Radiological criteria: new pulmonary infiltrate or worsening of a pre-existing pulmonary infiltrate on chest imaging. * No alternative diagnosis considered more likely to explain the clinical presentation, according to the treating physician. Exclusion Criteria: * Charlson Comorbidity Index ≥ 5. * Imminent death with a life expectancy \< 24 hours. * Admission to the intensive care unit (ICU) directly from the Emergency Department or within the first 24 hours after admission to the hospital ward. * Diagnosis of a solid-organ or hematologic malignancy with active oncologic treatment within the previous 3 months. * Immune-mediated disease treated with immunosuppressive or immunomodulatory drugs. * Transplant recipient. * Treatment with prednisone ≥ 20 mg/day (or equivalent) for ≥2 weeks. * Human immunodeficiency virus (HIV) infection with an absolute CD4 count \< 200 cells/µL. * Profound neutropenia (\< 100 cells/µL). * Refusal to participate in the study or concurrent participation in another study. * Previous inclusion in this study.