This study explores if the antibiotic **Azithromycin (AZ)** can help preschoolers with **severe wheezing**. Wheezing is a whistling sound made when breathing. The study is **double-blind**, meaning neither the doctors nor the participants know who is receiving the actual medicine or a **placebo** (a fake treatment). Participants will take AZ once daily for 5 days. The study will check if AZ helps reduce wheezing, especially for kids with certain bacteria in their noses.
Families will keep an **Asthma Flare-up Diary for Young Children (ADYC)** to record daily symptoms. Some kids will have two extra check-ups after the initial visit to see how they respond to the medicine. **Eligibility** includes children aged 18-60 months with wheezing verified by medical professionals. Kids with recent infections or certain medical conditions can't join.
- The study will last for about 21 days, with 3 planned visits for some participants.
- Participants must record symptoms daily using a diary.
- New medicines or treatments cannot be used 30 days before the study.