Serum KL-6 protein has been described as a biomarker of epithelial lung injury in Respiratory Syncytial Virus bronchiolitis. The investigators can imagine that epithelial injury intensity has consequences on immediate and later respiratory prognosis. Furthermore, this prognosis seems to be different according to the respiratory causative virus. The investigators propose to study, during an epidemic season, the correlation between KL-6 levels and clinical severity, and the type of viral infection.

Prospective, monocentric, case-control and transversal study Primary end-point: correlation between serum KL-6 level and severity of the bronchiolitis, evaluated by a clinical scoring system established at the time of the admission in Paediatric Emergency Unit Secondary end-points: respiratory virus detected by EIA and RT-PCR, phylogenetic study of rhinovirus, length of hospitalisation, immediate morbidity and mortality, risk of asthma at the age of three years old.

Inclusion Criteria:

• Cases: Inaugural acute bronchiolitis in infant aged under 1 year; bronchiolitis is defined by rhinorrhea and/or cough, dyspnea, associated with clinical or radiological distension, wheezing or crackling or brake expiratory.
• Controls: Infant aged under 1 year with blood sample test performed for a non-infectious disease (preoperative assessment)

Exclusion Criteria:

• Cases: bronchopulmonary dysplasia, prematurity, cystic fibrosis, immunodeficiency, primary ciliary dyskinesia, congenital cardiopathy, use of corticotherapy the week between inclusion
• Controls: infectious documented disease, respiratory symptoms

infants aged under 1 year