The purpose of this study is to determine whether nebulized hypertonic saline solution reduces the admission rate 48 hours after initial treatment in the emergency department, when compared to normal saline solution (control).

Acute viral bronchiolitis remains a significant cause of hospitalization and to date, no treatment reduce the rate of hospitalization. The only accepted treatment for bronchiolitis is nasal cleaning, hydration and for hospitalized hypoxemic infants, oxygen administration.

Several studies shown that nebulization of hypertonic saline solution reduce length of stay in hospital for hospitalized infant but effect on rate of hospitalization remains unclear.

The investigators propose a randomized double blind multicenter clinical trial on infants 6 weeks to 12 months old with moderate or severe bronchiolitis, in 21 emergency departments of hospitals situated France, during 2 winter seasons.

The investigators hypothesize that infants with bronchiolitis treated with nebulized hypertonic 3% saline solution would have less risk of being hospitalized. Our principal objective is to determine if nebulized 3% hypertonic saline solution reduces admission rate 24 hours after treatment compared to placebo.

Secondary objectives are to compare between groups intensity of respiratory symptoms measured by RDAI clinical score, duration of symptoms, length of hospital stay for hospitalized infants, adverse effects and health care utilization.

Patients presenting to the Emergency Department with a diagnosis of moderately severe bronchiolitis will be approached for entry into the study. After the initial routine assessment, informed consent will be obtained and the infant will be randomized to receive treatment in a double-blinded fashion 4 ml of nebulized study solution either 3% hypertonic saline (HS, study group) or 0.9% saline (NS, control group) every 20 minutes for a total of 2 doses. After an observation period of 20 minutes following the last dose, the infant will be reassessed by the attending physician in the ER for disposition (admit, discharge home). All subsequent therapy, if needed, will be at the sole discretion of the attending physician. The family of each recruited subject will be contacted by phone 2, 7, 14 and 28 days later to assess resolution of symptoms.

Clinical response to the above treatment will also be determined independently by the study physician utilizing a standardized respiratory scoring system, the Respiratory Distress Assessment Instrument (RDAI), at study entry and after each nebulization. The primary outcome measure is the rate of admission to hospital between the study and control groups 24 hours after inclusion. Secondary outcomes measure will involve the assessment of change in the RDAI between study entry and post-treatment, adverse effects, length of stay for hospitalized infant and health care utilization.

Inclusion Criteria:

• Age 6 weeks through 12 months
• First moderate to severe episode of acute viral bronchiolitis (history of viral upper respiratory tract infection plus wheezing and/or crackles on chest auscultation with respiratory distress ).
• Admission in Emergency Department
• Parental/guardian permission (informed consent)

Exclusion Criteria:

• prematurity < 37 weeks
• artificial ventilation in the neonatal period
• Chronic lung or heart disease
• history of immunodeficiency
• past use of nebulized HS
• initial need for intensive care of assisted ventilation
• Non-French speaking parent/guardian