Risk factors

Bronchiolitis typically affects children under the age of 2 years. Infants younger than 3 months of age are at greatest risk of getting bronchiolitis because their lungs and immune systems aren't yet fully developed.

Other factors that are linked with an increased risk of bronchiolitis in infants and with more-severe cases include:

• Premature birth
• Underlying heart or lung condition
• Depressed immune system
• Exposure to tobacco smoke
• Never having been breast-fed (breast-fed babies receive immune benefits from the mother)
• Contact with multiple children, such as in a child care setting
• Spending time in crowded environments
• Having siblings who attend school or get child care services and bring home the infection