This is an ambispective observational case-control study evaluating respiratory exacerbations in pediatric patients affected by bronchopulmonary dysplasia (BPD) compared with children without BPD. The study includes a retrospective cohort (January 2020 to September 2025) and a prospective cohort (from study approval to December 2030). Patients admitted to the Pediatric Emergency Department or Pediatric Unit for lower respiratory tract infections will be consecutively enrolled and managed according to standard clinical practice.

Inclusion Criteria:

• Corrected age ≥30 days and ≤7 years Acute lower respiratory tract infection

At least one of:

tachypnea for age SpO2 <94% increased work of breathing Gestational age <32 weeks Diagnosis of bronchopulmonary dysplasia according to NICHD 2018 definition

Exclusion Criteria:

• Grade ≥3 intraventricular hemorrhage Major congenital heart disease Neuromuscular disorders Chromosomal/genetic syndromes Primary pulmonary diseases Major skeletal dysplasia

Children with bronchopulmonary dysplasia and respiratory exacerbation, and Children without bronchopulmonary dysplasia admitted for respiratory exacerbation.