What age group is most commonly affected by bronchiolitis?

Bronchiolitis primarily affects infants, particularly those under the age of 2, making this age group the most commonly affected. This condition is typically caused by viral infections, with respiratory syncytial virus (RSV) being the most prevalent culprit. The anatomy and immune system of infants create a situation where they are more vulnerable to such infections, leading to the inflammation of the small air passages in the lungs.

Newborns can be included within the broader category of infants under 2 years; however, the highest incidence is observed in infants between 2 and 6 months of age. As children grow older, their airways enlarge, and their immune systems develop, making them less susceptible to bronchiolitis. Therefore, focusing on infants specifically allows for a more accurate representation of the demographic most affected, reinforcing why this is the correct answer.