Clinical meaning
RSV infects bronchiolar epithelial cells via fusion protein-mediated entry, causing necrosis, ciliary destruction, peribronchiolar lymphocytic infiltration, submucosal edema, and mucus hypersecretion. In infants, bronchiolar lumens are less than 1 mm; even 1 mm of circumferential edema reduces cross-sectional area by approximately 75%. A ball-valve mechanism develops where air enters on inspiration but becomes trapped on expiration, causing hyperinflation, air trapping, ventilation-perfusion mismatch, and hypoxemia. The immature infant immune response produces an exaggerated inflammatory reaction with neutrophil and eosinophil recruitment, worsening airway obstruction.
Diagnosis & workup
Diagnostics & workup: - Clinical diagnosis based on history and physical examination (no routine labs required) - Pulse oximetry for continuous SpO2 monitoring (most important objective measure) - Nasal wash or nasopharyngeal aspirate for RSV rapid antigen testing or PCR (guides cohorting, not treatment) - Chest X-ray only if diagnosis is uncertain or complications suspected (typically shows hyperinflation, peribronchial thickening, patchy atelectasis) - ABG only for impending respiratory failure (rising PaCO2 indicates fatigue) - CBC and CRP are NOT routinely recommended (do not change management)