A 3-month-old infant presents with a 3-day history of coryza, low-grade fever, and increasing respiratory distress with audible wheeze and poor feeding. On examination, the respiratory rate is 65/min, there are subcostal recessions, nasal flaring, and widespread inspiratory crackles and expiratory wheezes on auscultation. Oxygen saturation is 91% in air. What is the most likely diagnosis?