What is the most common cause of croup?

Updated: Oct 09, 2019
  • Author: Germaine L Defendi, MD, MS, FAAP; Chief Editor: Russell W Steele, MD  more...
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Parainfluenza viruses (types 1, 2, 3) are responsible for about 80% of croup cases, with parainfluenza types 1 and 2, accounting for nearly 66% of cases. Type 3 parainfluenza virus causes bronchiolitis and pneumonia in young infants and children. Type 4 parainfluenza virus, with subtypes 4A and 4B, is not as well understood and tends to be associated with a milder clinical illness.

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