**Abstract**

Acute bronchiolitis, which is the most common acute lower respiratory system disease, is resulting in significant morbidity and mortality in children less than 2 years. Respiratory syncytial virus (RSV) is the most common causative pathogen for over 30 million new acute lower respiratory infection episodes in children under 5 years of age. Rhinovirus, adenovirus, influenza virus, parainfluenza, and other respiratory viruses also cause acute bronchiolitis as the sole pathogen or as coinfection with or without RSV. Cardiovascular disease, chronic pulmonary disease, immunodeficiency, and premature birth are important risk factors for hospitalization and increase the risk of acute bronchiolitis-associated respiratory failure or even death. Bronchiolitis is a clinical diagnosis that varies from mild illness to severe respiratory failure. The severity of bronchiolitis is evaluated with several parameters including wheezing, retraction, respiratory rate, and general situation. However, the most important clinical finding is the presence or absence of hypoxemia and whether the patient can tolerate respiratory distress. Fluid support and oxygen supplementation by nasal cannula, face mask, or head box are critical for the treatment of bronchiolitis. Commonly used bronchodilators, corticosteroids, ribavirin, and antibiotics have not been shown to be effective in improving the clinical course of the bronchiolitis.

**Keywords:** acute bronchiolitis, infant, RSV
