Azithromycin to Prevent Wheezing Following Severe RSV Bronchiolitis-II

Inclusion Criteria

• Age: 1-18 months.
• Hospitalization for the first episode of RSV bronchiolitis.
• Confirmed RSV infection by positive nasal swab results (PCR assay and/or direct antigen detection).
• At least two of the following symptoms/signs of bronchiolitis: respiratory rate greater than 40 breaths/minute; cough; wheezing; audible rales, crackles, and/or rhonchi; paradoxical chest movements (retractions)28.
• Duration of respiratory symptoms from onset of symptoms of the current illness to admission is 120 hours (5 days) or less.
• Randomization can be performed within 168 hours (7 days) from onset of symptoms.
• Willingness to provide informed consent by the child's parent or guardian.

Exclusion Criteria

• Prematurity (gestational age < 36 weeks).
• Presence or history of other significant disease (CNS, lung, cardiac, renal, GI, hepatic disease, hematologic, endocrine or immune disease). Children with atopic dermatitis and/or food allergy will not be excluded from the study.
• Clinically significant gastroesophageal reflux currently treated with a daily anti-reflux medication (anti- H2 or PPI).
• The child has significant developmental delay/failure to thrive, defined as weight < 3% for age and gender.
• History of previous (before the current episode) wheeze or previous (before the current episode) treatment with albuterol.
• History of previous treatment with corticosteroid (systemic or inhaled) for respiratory issues.
• Treatment (past or present) with montelukast.
• Treatment with any macrolide antibiotic (azithromycin, clarithromycin or erythromycin) over the past 4 weeks or current treatment with any macrolide antibiotic. Current or prior treatment with non-macrolide antibiotic is not an exclusion criterion.
• Chronic treatment with any daily medication other than vitamins or nutritional supplements. Although routine vitamin D supplement (400 IU per day) is not an exclusion criterion, high dose vitamin D supplements are not allowed.
• Participation in another clinical trial.
• Participant requires invasive mechanical ventilation due to RSV bronchiolitis.
• Evidence that the family may be unreliable or non-adherent, or has definitive plans to move from the clinical center area before trial completion.
• Contraindication of use of azithromycin or any other macrolide antibiotics such as history of allergic reaction (or other adverse reaction) to these antibiotics.
• Diagnosis of asthma.
• Treatment with other medication that may cause QT interval prolongation.