The goal of this randomized clinical trial is to investigate the optimal supportive treatment of bronchiolitis in infants from 0-12 months of age. The main question[s] it aims to answer are:

• To investigate whether isotonic saline should be used as supportive treatment for children with bronchiolitis, and if so, identify the optimal route of administration. The primary outcome is duration of hospitalization.
• To investigate the current epidemiology of the viral pathogens causing bronchitis in children in Denmark, and to assess whether children infected with specific pathogens might benefit from treatment with isotonic saline.

The children are randomized after inclusion through computer randomization to one of the 3 arms in the study:

1. Nebulized isotonic saline
2. Nasal irrigation with isotonic saline
3. No treatment with saline

The investigators will compare treatment with saline (both methods) with no treatment, and the investigators will also compare the two methods of delivery of saline (nebulized vs. nasal irrigation).

Design: An investigator-initiated, multicenter, open label, three-arm randomized, controlled non-inferiority trial.

Study sites: Seven pediatric departments in eastern Denmark (Slagelse Hospital, Holbæk Hospital, Zealand University Hospital Roskilde, Copenhagen University Hospital Hvidovre, Copenhagen University Hospital Herlev, Nordsjaellands Hospital, and Nykoebing Falster Hospital).

Participants: Children aged 0-12 months admitted to a pediatric department or emergency department in eastern Denmark with bronchiolitis, whose parents provide informed consent for participation.

Randomization: Participating children are randomized 1:1:1 through computer randomization to either nebulized isotonic saline, nasal irrigation with isotonic saline or no isotonic saline therapy at all. Participating children will have a nasal sample collected and tested for a panel of viral pathogens. Excess material (1 ml nasal lining fluid) from upper airway respiratory samples will be stored in a research biobank until 31.12.2030 and used for sub-phenotyping of bronchiolitis and for developing personalized treatment and prediction of later asthma by means of host transcriptomics and metabolomics, 16S sequencing of the airway microbiome and meta-transcriptomics.

All other treatment is given according to standard of care guidelines.

Sample size: By including 249 children in total (83 in each arm) the investigators can prove non-inferiority of nasal irrigation or nebulized saline relative to no saline with a non-inferiority limit of 12 hours admission, alpha 2.5% and a power of 80%. The investigators aim to include 300 children in total to account for dropouts.

Recruitment: Children will only be included if both parents provide informed consent.

Perspectives: This study may improve current practice for supportive treatment of children with bronchiolitis. If saline is found to be helpful, it may be implemented into global guidelines. If no effect of saline is found, physicians may stop spending resources and manpower on an ineffective and potentially unpleasant treatment. Second, if saline is effective, but nasal irrigation proves to be non-inferior to nebulization, it may also reduce the workload of nurses, and possibly duration of hospitalization, because the treatment can be delivered by the parents at home. Moreover, the parents are empowered to manage their child's illness themselves, potentially improving the experience of parents as well as the affected child.

Inclusion Criteria:

• Children aged 0-12 months, whose parents give informed consent to participate, with symptoms of bronchiolitis including at least one of:

  • Runny nose
  • Dry and persistent cough
  • Labored breathing (tachypnea, retractions, nasal flaring)
  • Grunting
  • Cyanosis or apnea
  • Wheezing or crackles on auscultation
  • O2 saturations below 92 %
  • Difficulties feeding

Exclusion Criteria:

• Children with cystic fibrosis or other serious congenital lung diseases
• Children in whom treatment with short-acting beta-2 agonist is initiated (as this is delivered in nebulized isotonic saline).

We have planned to share all IPD with other researchers upon request.

We have planned to share all IPD with other researchers upon request 5 years after publication.

Researchers who request access.

Outcome assessor will receive anonymized data for analysis.