Which virus is the most likely cause of bronchiolitis in toddlers?

Respiratory Syncytial Virus (RSV) is identified as the most common cause of bronchiolitis in toddlers. This viral infection primarily affects the small airways (bronchioles) in the lungs and is particularly prevalent in children under the age of two. RSV is known for its high morbidity rate in this age group and is responsible for a significant number of hospital admissions associated with lower respiratory tract infections.

The pathophysiology of RSV involves the virus leading to inflammation and obstruction in the small airways, resulting in respiratory distress, wheezing, and difficulty in breathing. The peak incidence of RSV infections occurs during the late fall and winter months, aligning with seasonal patterns of viral respiratory infections in children.

In contrast, while other viruses such as adenovirus, rhinovirus, and Haemophilus influenzae type B can cause respiratory symptoms, they are less commonly associated with bronchiolitis specifically in toddlers compared to RSV. Adenovirus and rhinovirus tend to cause a broader range of respiratory illnesses, and Haemophilus influenzae type B is more known for causing bacterial infections rather than viral bronchiolitis. Thus, RSV stands out as the primary etiological agent in this context.