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.