Greatest risk factors for progression to respiratory failure in bronchiolitis include

• A. First months of life, prematurity, lung disease, congenital heart disease, immunodeficiency.
• B. Age older than 2 years.
• C. Exclusive bottle feeding.
• D. Urban residence.

Answer: (A)

The key idea here is what factors make bronchiolitis more likely to progress to respiratory failure. The combination listed—being in the first months of life, prematurity, existing lung disease, congenital heart disease, and immunodeficiency—identifies infants with the least respiratory reserve and the most vulnerability to viral injury. Very young infants have tiny airways and less ability to clear mucus and edema, so RSV- or other viral bronchiolitis can quickly impair gas exchange. Prematurity means underdeveloped lungs and airway structures, increasing risk of severe hypoxemia. Chronic lung disease and congenital heart disease reduce the heart-lung system’s ability to meet oxygen demands during illness. Immunodeficiency impairs the body’s ability to control infection, leading to more severe disease.

The other options don’t fit because older than 2 years is not a typical risk for bronchiolitis progression, exclusive bottle feeding is not a known risk (breastfeeding is generally protective), and urban residence doesn’t inherently raise the risk of progression to respiratory failure.