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Like influenza (flu) and some forms of the common cold, respiratory syncytial virus (RSV) is a respiratory virus that can cause lung infections. It’s often a routine childhood illness that runs its course without requiring a doctor’s attention, but it’s also the most common cause of bronchiolitis (inflammation of the small airways in the lung) and pneumonia in children less than 1 year of age.

RSV exists all over the world, but it’s active at different times of the year depending on geographical climate. Temperate regions, including most of the United States, experience RSV season during the late fall, winter, and early spring months. Tropical regions see peaks in RSV infections during the rainy season.

Last Updated February 15, 2013

Last Reviewed February 15, 2013