Acute bronchiolitis is a common disease in children under the age of two, caused mainly by the respiratory syncytial virus (RSV). Furthermore, given the same medical history, it is still very difficult to predict the course and severity of the infection at the onset of symptoms, Some studies have highlighted the importance of the microbiota (intestinal, oral or nasopharyngeal) and of the immune response to RSV in children, We will include 80 children under 2 years old with hospitalized bronchiolitis and non-hospitalized bronchiolitis. Oral, nasal and stool samples will be taken to study the various microbiota in search of dysbiosis. A capillary blood sample will be taken for immune studies.