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

Bronchiolitis is a very common viral infection most often caused by respiratory syncytial virus. It is most often seen in the winter months with symptoms of wheezing, hypoxia, and respiratory distress seen in younger children; often an older sibling has milder, upper respiratory symptoms. Premature infants, infants with congenital heart disease, infants with a variety of lung disorders, and infants with immune system defects are at higher risk of severe complications. Diagnosis is made by clinical history and/or detection of the viral antigen in nasal secretions; treatment is supportive.