**Question:** A preterm infant is now 7 weeks old. She was intubated for 2 weeks and was weaned off oxygen at 3 weeks of age. You are about to leave your office for the Thanksgiving holiday when the emergency room calls to tell you she has recent onset of hypoxia, respiratory distress, wheezes, and runny nose. A chest radiograph reveals patchy infiltrates and hyper-expansion in both lung fields. The newborn's 2-year-old sibling has an upper respiratory infection. For the mentioned clinical scenario, select the most likely diagnosis

A. Respiratory distress syndrome (RDS)
B. Bronchopulmonary dysplasia (BPD)
C. Congenital heart disease (CHD)
D. Respiratory syncytial virus (RSV) infection

**Correct Answer:** D. Respiratory syncytial virus (RSV) infection

**Core Concept:** The scenario involves a preterm infant with recent onset of respiratory distress symptoms, chest radiograph findings, and a sibling with an upper respiratory infection. This combination of symptoms and clinical context strongly suggests a viral respiratory infection as the underlying cause.

**Why the Correct Answer is Right:**

The correct answer is respiratory syncytial virus (RSV) infection because:

1. **RSV is a common respiratory virus:** RSV is one of the most common causes of lower respiratory tract infections in infants, particularly preterm infants. It is highly prevalent during autumn and winter seasons and can cause severe respiratory distress, making it the most likely diagnosis in this case.
2. **Radiographic findings:** The chest radiograph shows patchy infiltrates and hyper-expansion in both lung fields, which are consistent with respiratory distress due to viral infection.
3. **Sibling with upper respiratory infection:** Having an infected sibling increases the probability of RSV infection, as the virus can be transmitted easily within a family environment.

**Why Other Options are Incorrect:**

A. Respiratory distress syndrome (RDS) is a non-infectious condition caused by lack of surfactant production in premature infants, which leads to respiratory distress. It is not a viral infection and does not have the same radiographic findings as described in the question.
B. Bronchopulmonary dysplasia (BPD) is a long-term complication of premature birth, characterized by impaired lung development and chronic lung disease. It is not a viral infection and does not present with respiratory distress symptoms in this context.
C. Congenital heart disease (CHD) is a structural heart defect present at birth, which typically does not cause respiratory distress symptoms and does not have the described radiographic findings.

**Clinical Pearls:**

1. RSV is a common cause of severe lower respiratory tract infections in infants, particularly preterm infants.
2. The presence of a sibling with upper respiratory infection increases the likelihood of RSV transmission within the family environment.
3. Chest radiograph findings of patchy infiltrates and hyper-expansion in both lung fields are consistent with viral respiratory illness.

In conclusion, considering the clinical context and radiological findings, respiratory syncytial virus (RS