The goal of the present randomised controlled clinical trial is to compare the efficacy of a 30-minute exposition to cold, atmospheric, outdoor air on the severity of croup symptoms with exposition to indoor room air in children with mild to moderate croup receiving a single dose of dexamethasone during winter croup outbreaks.

Croup is a viral laryngitis that represents the most common cause of acute upper airway obstruction in children. It is therefore a frequent reason for emergency department visits. The benefit of dexamethasone on croup symptoms is well established with an onset of action of at least 30 minutes. Various non-pharmacological measures, including exposition to cold air, are also thought to be effective in reducing the severity of symptoms, although this has not been demonstrated yet in the current scientific literature. The aim of the present study is to evaluate the efficacy of exposition to cold air on the symptoms of croup in children.

The investigators designed a prospective, open-label, single centre randomised controlled trial to evaluate the effect of exposition to cold air on the symptoms of croup in children.

The study was performed during autumn and winter croup outbreaks when outdoor air temperature was <10°C (<50°F). Participants were infants and children aged 3 months to 10 years presenting to the pediatric emergency department of our institution. Inclusion criteria were patients presenting with mild to moderate croup symptoms with Westley croup scores > or=2 (to permit a clinically relevant reduction in the Westley croup score of at least 2 points from baseline at 30 minutes), diagnosed by a triage nurse and confirmed by a senior attending pediatric emergency physician. Exclusion criteria were history or physical examination suggesting any other diagnosis, severe croup requiring immediate nebulised epinephrine, chronic respiratory disease (except asthma), underlying airway abnormalities, immunodeficiency; and contraindication to steroids. According to the recommended standards of care, all children with croup were administered a standard 0·6 mg/kg/dose oral dexamethasone at triage.

Participants were randomly allocated either to the outdoor cold air exposition group or to the indoor group allocation using a single, constant 1:1 allocation ratio. Demographic data, previous exposition to cold air before presentation at pediatric emergency department, as well as vital signs and Westley croup score on arrival, and after 30 and 60 minutes, were recorded. Parents were reached by phone 7 days after the initial visit to assess the child's clinical outcome and the final diagnosis, as well as the need for further consultation or hospitalization in the meantime.

Inclusion Criteria:

- children from 3 months to 10 years with clinical signs of croup and Westley croup score > or =2

Exclusion Criteria:

• Need for close monitoring
• Need for nebulized epinephrine
• History or physical examination suggesting any other diagnosis
• Chronic respiratory disease (except asthma)
• Underlying airway abnormalities
• Immunodeficiency
• Contraindication to steroids

Deidentified Individual Participant Data will be available from the corresponding author upon reasonable request, recognizing that these data will only provide results for the current trial and not for future trials. Only deidentified/anonymized data will be shared.

6 month to 5 years after publication of results.

Data will be made available from the corresponding author upon approval of a proposal and after a signed data access agreement.

Deidentified participant data will be made available to qualified external researchers who will use them according to their Institutional Review Board.

Data will be made available for a specified research purpose. The request proposal should include participation of a statistician.