In a child 1 years the commonest cause of resp. Infection with wheeze is –
**Core Concept**
Respiratory infections with wheezing in children are a common presentation in pediatric emergency medicine. The underlying pathophysiology involves inflammation and airway obstruction, often precipitated by viral infections.
**Why the Correct Answer is Right**
In a 1-year-old child, respiratory syncytial virus (RSV) is the most common cause of lower respiratory tract infections, including bronchiolitis and pneumonia, which often present with wheezing. RSV infection triggers an inflammatory response in the airways, leading to increased mucus production, airway edema, and subsequent wheezing. This is due to the binding of RSV to the host cell receptors, particularly the sialic acid receptors on the surface of respiratory epithelial cells.
**Why Each Wrong Option is Incorrect**
**Option A:** Adenovirus can also cause respiratory infections with wheezing, but it is less common than RSV in children under 1 year.
**Option B:** Influenza virus typically presents with fever, cough, and sore throat, rather than isolated wheezing.
**Option C:** Parainfluenza virus is a common cause of croup, which presents with a distinctive barking cough and stridor, rather than wheezing.
**Clinical Pearl / High-Yield Fact**
RSV infection is often seasonal, peaking during the winter months, and can be prevented with palivizumab prophylaxis in high-risk infants.
**Correct Answer: C. Parainfluenza virus**