A 5-year-old child complains of a cough that gradually intensifies. According to the patient's medical history, the onset of the disease was 12 days ago. Objectively, the body temperature is 37.1°C, the skin is pale, the oropharyngeal mucosa is pale pink. There is a small ulcer on the frenulum of the tongue. Coughing fits occur up to 20 times per 24 hours and can be characterized by a series of cough impulses, followed by a wheezing inhalation. A coughing fit ends with the expectoration of vitreous sputum. Auscultation detects harsh respiration and dry (sometimes wet) crackles in the lungs. Chest X-ray shows a horizontal position of the ribs, increased transparency of the lungs, and an expanded pulmonary pattern in the roots of the lungs. Complete blood count: leukocytosis 23.109/L, eosinophils 1%, band neutrophils 3%, segmented neutrophils _23%, lymphocytes - 70%, monocytes - 3%, ESR - 3 mm/hour. What is the most likely diagnosis in this case?