Bronchiolitis obliterans (BO) is an irreversible chronic obstructive pulmonary pathology leading to obstruction and/or obliteration of the small airways. In children, the most common form of BO occurs following a serious lower respiratory tract infection. This is a rare complication; the incidence is unknown. The diagnosis, often late, is made on clinical, spirometric and radiological arguments. The pathophysiology would be linked to damage to the airway epithelium. PIBO is most commonly associated with adenovirus (ADV) infection (serotypes 3, 7, 11 and 21) but also other viruses such as rhinovirus (RV). The treatment of PIBO is not clearly established, it remains empirical.

The research hypothesis is that the morphology of the nasal epithelium of children with ADV or RV infection is different for those progressing to PIBO. The main objective of the proposed observational study is to characterize damage to the respiratory epithelium in these children.

This is a single-center prospective longitudinal study (AP-HM), in children aged 1 month to 6 years, comparing children hospitalized for lower respiratory infection by ADV or RV progressing or not to PIBO. All children included will have a nasal swab and brushing on D0. Children developing PIBO will have nasal brushing with bronchial endoscopy with bronchial biopsies and bronchoalveolar washing at the time of PIBO diagnosis and again at M6 in case of partial response to treatment.

This is therefore a pilot study aimed at defining damage to the respiratory epithelium in children with PIBO following an ADV or RV infection and the role of respiratory epithelial cells in PIBO.

Inclusion Criteria:

1. Children from 1 month to 6 years hospitalized at the Timone Enfant University Hospital
2. Diagnosis of an adenovirus or rhinovirus respiratory infection confirmed on a nasal swab, made upon arrival as part of the child's initial care
3. Consent form read, understood, approved and signed by parents before any study procedure
4. Affiliation to a social security scheme or beneficiary of such a scheme

The inclusion criteria for children who were not hospitalized when diagnosed with an adenovirus and rhinovirus respiratory infection at the Timone Enfant University Hospital are:

1. Children from 1 month to 6 years old transferred to the Timone Enfant University Hospital

2. Show the following signs:

   has. Clinical: clinical signs persist 6 weeks after a viral infection: tachypnea, wheezing and/or persistent hypoxemia b. Scan: mosaic appearance +/- bronchiectasis, atelectasis vs. +/- EFR if performed: obstructive ventilatory disorder not or only slightly reversible after bronchodilators

3. Consent form read, understood, approved and signed by parents before any study procedure

4. Affiliation to a social security scheme or beneficiary of such a scheme

Exclusion Criteria:

1. Refusal of participation in the study by the family will be a reason for non-inclusion, as well as in the absence of parental authority.
2. The existence of an underlying chronic pulmonary pathology (e.g. cystic fibrosis, ciliary dyskinesia).
3. A coagulation pathology.