Features of bronchiolitis are a) Caused by R.S.V. b) Wheeze present c) Pulmonary edema common d) Seen in immunocompromised hosts e) Common age groups is from 5 to 15 years age

**Core Concept**
Bronchiolitis is a **respiratory illness** characterized by inflammation and obstruction of the small airways. It is most commonly caused by **respiratory syncytial virus (R.S.V.)**. The condition primarily affects young children.

**Why the Correct Answer is Right**
The correct answer is related to the fact that bronchiolitis is indeed **caused by R.S.V.**, which is a major pathogen in this context. R.S.V. infection leads to inflammation and increased mucus production in the small airways, resulting in **respiratory symptoms**.

**Why Each Wrong Option is Incorrect**
**Option B:** Wheeze can be present but is not a universal feature, and its absence does not rule out bronchiolitis.
**Option C:** Pulmonary edema is not a common feature of bronchiolitis.
**Option D:** While immunocompromised hosts can be affected, bronchiolitis is not exclusive to them.
**Option E:** The common age group for bronchiolitis is actually from **6 months to 2 years**, not 5 to 15 years.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that **R.S.V.** is the most common cause of bronchiolitis, especially in children under 2 years of age.

**Correct Answer:** A. Caused by R.S.V.